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Columbia  Untfataftg  JBhlogical  Sbzihs 

EDITED    BY 
HENRY    FAIRFIELD   OSBORN 

AND 

EDMUND    B.    WILSON 

I.  FROM  THE  GREEKS  TO  DARWIN 

By  Henry  Fairfield  Osborn 

II.  AMPHIOXUS  AND  THE  ANCESTRY  OF  THE  VERTEBRATES 

By  Arthur  Willey 

III.  FISHES.   LIVING  AND   FOSSIL.      An  Introductory  Study 

By  Bashford  Dean 

IV.  THE   CELL   IN   DEVELOPMENT  AND   INHERITANCE 

By  Edmund  B.  Wilson 

V.    THE   FOUNDATIONS   OF  ZOOLOGY 
By  W.  K.  Brooks 

VI.    THE   PROTOZOA 

By  Gary  N.  Calkins 

VII.    REGENERATION 

By  T.  H.  Morgan 

VIII.    THE   DYNAMICS   OF  LIVING   MATTER 
By  Jacques  Loeb 

IX.    STRUCTURE  AND   HABITS  OF  ANTS.    (In  preparation) 
By  W.  M.  Wheeler 

X.    BEHAVIOR   OF  THE   LOWER   ORGANISMS. 
By  H.  S.  Jennings 


BEHAVIOR   OF   THE    LOWER   ORGANISMS 


► 


T&'t&^^f 


COLUMBIA    UNIVERSITY  BIOLOGICAL   SERIES.     X. 


BEHAVIOR  OF  THE   LOWER 

ORGANISMS 


BY 


H.   S.   JENNINGS 

ASSISTANT   PROFESSOR    OF   ZOOLOGY   IN   THE 
UNIVERSITY   OF   PENNSYLVANIA 


Ncfo  gork 
THE   COLUMBIA   UNIVERSITY   PRESS 

THE  MACMILLAN   COMPANY,  Agents 

LONDON:   MACMILLAN  &   CO.,   Ltd. 

1906 

All  rights  reserved 


Copyright,  1906, 
By  THE   MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  July,  1906. 


Nortaooo  IPresB 

J.  S.  Cushing  &  Co.  —  Berwick  &  Smith  Co. 

Norwood,  Mass.,  U.S.A. 


PREFACE 

The  objective  processes  exhibited  in  the  behavior  of  the  lower 
organisms,  particularly  the  lower  animals,  form  the  subject  of  the 
present  volume.  The  conscious  aspect  of  behavior  is  undoubtedly 
most  interesting.  But  we  are  unable  to  deal  directly  with  this  by 
the  methods  of  observation  and  experiment  which  form  the  basis  for 
the  present  work.  Assertions  regarding  consciousness  in  animals, 
whether  affirmative  or  negative,  are  not  susceptible  of  verification. 
This  does  not  deprive  the  subject  of  consciousness  of  its  interest,  but 
renders  it  expedient  to  separate  carefully  this  matter  from  those 
which  can  be  controlled  by  observation  and  experiment.  For  those 
primarily  interested  in  the  conscious  aspects  of  behavior,  a  presenta- 
tion of  the  objective  facts  is  a  necessary  preliminary  to  an  intelligent 
discussion  of  the  matter. 

But  apart  from  their  relation  to  the  problem  of  consciousness 
and  its  development,  the  objective  processes  in  behavior  are  of  the 
highest  interest  in  themselves.  By  behavior  we  mean  the  general 
bodily  movements  of  organisms.  These  are  not  sharply  distin- 
guishable from  the  internal  physiological  processes ;  this  will  come 
forth  clearly  in  the  present  work.  But  behavior  is  a  collective  name 
for  the  most  striking  and  evident  of  the  activities  performed  by 
organisms.  Its  treatment  as  subsidiary  to  the  problems  of  con- 
sciousness has  tended  to  obscure  the  fact  that  in  behavior  we  have 
the  most  marked  and  in  some  respects  the  most  easily  studied  of 
the  organic  processes.  Such  treatment  has  made  us  inclined  to 
look  upon  these  processes  as  something  totally  different  from  the 
remainder  of  those  taking  place  in  organisms.  In  behavior  we  are 
dealing  with  actual  objective  processes  (whether  accompanied  by 
consciousness  or  not),  and  we  need  a  knowledge  of  the  laws  con- 
trolling them,  of  the  same  sort  as  our  knowledge  of  the  laws  of 
metabolism.  In  many  respects  behavior  presents  an  exceptionally 
favorable  field  for  the  study  of  some  of  the  chief  problems  of  life. 
The  processes  of  behavior  are  regulatory  in  a  high  degree.  Owing 
to  their  striking  character,  the  way  in  which  regulation  occurs  be- 
comes more  evident  than  in  most  other  fields,  so  that  they  pre- 
sent a  most  favorable  opportunity  for   study  of  this  matter.      To 


VI  PREFACE 

the  regulatory  aspect  of  behavior  special  attention  is  paid  in  the 
following  pages. 

The  modifiability  of  the  characteristics  of  organisms  has  always 
been  a  subject  of  the  greatest  importance  in  biological  science.  In 
most  fields  the  study  of  this  matter  is  beset  with  great  difficulties,  for 
the  modifications  require  long  periods  and  their  progress  is  not  easily 
detectible.  In  the  processes  of  behavior  we  have  characteristics  that 
are  modifiable  with  absolute  ease.  In  the  ordinary  course  of  be- 
havior variations  of  action  are  continually  occurring,  as  a  result  of 
many  internal  and  external  causes.  We  see  quickly  and  in  the  gross 
the  changes  produced  by  the  environment,  so  that  we  have  the  best 
possible  opportunity  for  the  study  of  the  principles  according  to 
which  such  changes  occur.  Permanent  modifications  of  the  methods 
of  action  are  easily  produced  in  the  behavior  of  many  organisms. 
When  we  limit  ourselves  to  the  subjective  aspect  of  these,  thinking 
only  of  memory,  or  the  like,  we  tend  to  obscure  the  general  problem 
involved.  This  problem  is :  What  lasting  changes  are  producible  in 
organisms  by  the  environment  or  otherwise,  and  what  are  the  princi- 
ples governing  such  modifications  ?  Perhaps  in  no  other  field  do  we 
have  so  favorable  an  opportunity  for  the  study  of  this  problem, 
fundamental  for  all  biology,  as  in  behavior.  There  seems  to  be  no 
a  priori  reason  for  supposing  the  laws  of  modification  to  be  different 
in  this  field  from  those  found  elsewhere.  The  matter  needs  to  be 
dealt  with  from  an  objective  standpoint,  keeping  the  general  problem 
in  mind. 

A  study  of  behavior  from  the  objective  standpoint  will  help  us 
to  realize  that  the  activities  with  which  we  deal  in  other  fields  of 
physiology  are  occurring  in  a  substance  that  is  capable  of  all  the 
processes  of  behavior,  including  thought  and  reason.  This  may  aid 
us  to  be  on  our  guard  against  superficial  explanations  of  physiological 
processes. 

But  the  chief  interest  of  the  subject  of  the  behavior  of  animals 
undoubtedly  lies,  for  most,  in  its  relation  to  the  development  of 
psychic  behavior,  as  shown  by  man.  The  behavior  of  the  lowest 
organisms  must  form  a  fundamental  part  of  comparative  psychology. 

In  the  special  field  of  the  behavior  of  the  lowest  organisms  the 
foundations  of  our  knowledge  were  laid  by  Verworn,  in  1889,  in  his 
"Psycho-physiologische  Protistenstudien."  Binet,  in  his  "Psychic 
Life  of  Micro-organisms"  (1889),  gave  a  most  readable  essay  on  the 
subject,  presenting  it  frankly  from  the  psychical  standpoint.  Lukas, 
in  his  "  Psychologie  der  niedersten  Tiere  "  (1905),  has  recently  again 
dealt  with  the  questions  of  consciousness  in  lower  animals,  the  treat- 
ment of  objective  processes  being  subsidiary  to  this  matter. 

The  present  work  was  designed  primarily  as  an  objective  descrip- 


PREFACE  vii 

tion  of  the  known  facts  of  behavior  in  lower  organisms,  that  might 
be  used,  not  only  by  the  general  reader,  but  also  as  a  companion 
in  actual  laboratory  experimentation.  This  description,  comprising 
Parts  I  and  II  of  the  present  work,  on  the  Protozoa  and  lower  Meta- 
zoa,  respectively,  was  made  as  far  as  possible  independent  of  any 
theoretical  views  held  by  the  writer ;  his  ideal  was  indeed  to  present 
an  account  that  would  include  the  facts  required  for  a  refutation  of 
any  of  his  own  general  views,  if  such  refutation  is  possible.  These 
designs  have  involved  a  fuller  statement  of  details,  with  sometimes 
their  repetition  under  new  experimental  conditions,  than  would  have 
been  necessary  if  the  theoretical  discussion  had  been  made  primary, 
and  only  such  facts  adduced  as  would  serve  to  illustrate  the  views 
advanced.  But  the  scientific  advantages  of  the  former  method  were 
held  to  outweigh  the  literary  advantages  of  the  latter. 

As  originally  written,  this  descriptive  portion  of  the  work  was 
more  extensive,  including,  besides  the  behavior  of  the  Protozoa  and 
Ccelenterata,  systematic  accounts  of  behavior  in  Echinoderms,  Ro- 
tifera,  and  the  lower  worms,  together  with  a  general  chapter  on  the 
behavior  of  other  invertebrates.  The  work  was  planned  to  serve  as 
a  reference  manual  for  the  behavior  of  the  groups  treated.  But  the 
exigencies  of  space  compelled  the  substitution  of  a  chapter  on  some 
important  features  of  behavior  in  other  invertebrates  for  the  system- 
atic accounts  of  the  three  groups  last  mentioned.  The  accounts  of 
the  Protozoa  and  of  the  Ccelenterata  as  representative  of  the  lowest 
Metazoa  remain  essentially  as  originally  written. 

After  this  objective  description  was  prepared,  the  need  was  felt 
for  an  analysis  of  the  facts,  such  as  would  bring  out  the  general 
relations  involved.  Part  III  is  the  result.  Thus  the  conclusions  set 
forth  in  Part  III  are  the  result  of  a  deliberate  analysis  of  the  facts 
presented  in  a  description  which  had  been  made  before  the  conclu- 
sions had  been  drawn.  The  selection  of  facts  set  forth  in  the  de- 
scriptive parts  of  the  work  has  therefore  been  comparatively  little 
affected  by  the  general  theories  held  by  the  writer.  The  loss  of 
unity  toward  which  this  fact  tends  has  perhaps  its  compensation  in 
the  impartiality  which  it  helps  to  give  the  descriptions. 

The  writer  is  conscious  of  the  necessarily  provisional  nature  of 
most  general  conclusions  at  the  present  stage  of  our  knowledge,  and 
the  analysis  given  in  Part  III  is  presented  with  this  provisional 
character  fully  in  mind.  The  reader  should  approach  it  in  a  similar 
attitude. 

Since  the  book  is  written  primarily  from  a  zoological  standpoint, 
it  would  be  appropriate  in  some  respects  to  entitle  it  "  Behavior  of 
the  Lower  Animals."  But  the  broader  title  seems  on  the  whole  best, 
since  the  treatment  of  unicellular  forms  involves  consideration  of 


viii  PREFACE 

many  organisms  that  are  more  nearly  related  to  plants  than  to 
animals. 

The  figures  have  been  drawn  for  the  present  work  by  my  wife. 
Figures  not  credited  to  other  authors  are  either  new  or  taken  from 
my  own  previous  works. 

The  author  is  much  indebted  to  the  Carnegie  Institution  of 
Washington  for  making  possible  a  year  of  uninterrupted  research, 
devoted  largely  to  studies  preliminary  to  the  preparation  of  this 
work  and  to  its  actual  composition.  He  is  further  indebted  for 
the  use  of  a  number  of  figures  first  published  by  the  Carnegie 
Institution. 

University  of  Pennsylvania, 
December  II,  1905. 


CONTENTS 
PART   I 

BEHAVIOR    OF   UNICELLULAR    ORGANISMS 

CHAPTER   I 

Behavior  of  Amceba 

PAGE 

1.  Structure  and  Movements  of  Amceba I 

2.  Reactions  of  Amceba  to  Stimuli 6 

A.  Reaction  to  Contact  with  Solids 6 

B.  Reactions  to  Chemicals,  Heat,  Light,  and  Electricity 9 

C.  How  Amceba  gets  Food      .         .         .         .         .         .         .         .         •         .12 

3.  Features  of  General  Significance  in  the  Behavior  of  Amoeba 19 

Literature 25 

CHAPTER   II 

Behavior  of  Bacteria 

1.  Structure  and  Movements 26 

2.  Reactions  to  Stimuli 27 

3.  General  Features  in  the  Behavior  of  Bacteria 37 

Literature 4° 

CHAPTER  III 

Behavior  of  Infusoria;    Paramecium 
Structure;  Movements;  Method  of  Reaction  to  Stimuli 

Introductory 41 

1.  Behavior  of  Paramecium;   Structure 41 

2.  Movements 44 

3.  Adaptiveness  of  the  Movements 45 

4.  Reactions  to  Stimuli         ............  47 

5.  "  Positive  Reactions  " 54 

Literature 5^ 

CHAPTER   IV 

Behavior  of  Paramecium  (continued) 
Special  Features  of  the  Reactions  to  a  Number  of  Different  Classes  of  Stimuli 

1.  Reaction  to  Mechanical  Stimuli 59 

2.  Reactions  to  Chemical  Stimuli 62 

ix 


£ 


X  CONTENTS 

PAGE 

3.  Reactions  to  Heat  and  Cold 70 

4.  Reaction  to  Light    .............  72 

5.  Orienting  Reactions,  to  Water  Currents,  to  Gravity,  and  to  Centrifugal  Force          .  73 

A.  Reactions  to  Water  Currents       .........  73 

B.  Reactions  to  Gravity  ...........  75 

C.  Reaction  to  Centrifugal  Force     .........  78 

6.  Relation  of  the  Orientation  Reactions  to  Other  Reactions 78 

Literature      ...............  79 


CHAPTER   V 

Behavior  of  Paramecium  (continued) 

Reactions  to  Electricity  and  Special  Reactions 

1.  Reactions  to  Electricity 80 

A.  Reaction  to  Induction  Shocks 81 

B.  Reaction  to  the  Constant  Current 83 

2.  Other  Methods  of  Reaction  in  Paramecium 89 

Literature 91 

CHAPTER   VI 
Behavior  of  Paramecium  (continued) 

Behavior  under  Two  or  More  Stimuli  ;    Variability  of  Behavior ;  Fission  and 
Conjugation  ;  Daily  Life  ;   General  Features  of  the  Behavior 

1.  Behavior  under  Two  or  More  Stimuli 92 

2.  Variability  and  Modifiability  of  Reactions 98 

3.  Behavior  in  Fission  and  Conjugation .  102 

4.  The  Daily  Life  of  Paramecium 104 

5.  Features  of  General  Significance  in  the  Behavior  of  Paramecium    ....  107 

A.  The  Action  System 107 

B.  Causes  of  the  Reactions,  and  Effects  produced  by  them      .         .         .         ,108 
Literature 109 


CHAPTER   VII 

Behavior  of  Other  Infusoria 

Action  Systems.     Reactions  to  Contact,  to  Chemicals,  to  Heat  and  Cold 

1.  The  Action  System "O 

A.  Flagellata m 

B.  Ciliata "3 

2.  Reaction  to  Mechanical  Stimuli       .         .         .         .         .         •         •         •         •         ■  Il7 

3.  Reaction  to  Chemicals 120 

4.  Reaction  to  Heat  and  Cold 124 

Literature I27 


COX  TEXTS 


XI 


CHAPTER   VIII 
Reactions  of  Infusoria  to  Light  and  to  Gravity 


Reactions  to  Light 

A.  Negative  Reaction  to  Light :   Stentor  azruleus 

B.  Positive  Reaction  to  Light :  Eugiena  viridis 

C.  Negative  and  Positive  Reactions  compared 

D.  Reactions  to  Light  in  Other  Infusoria 
Reaction  to  Gravity  and  to  Centrifugal  Force 


2. 


Literature 


PAGE 
128 
I  28 

134 
141 
141 

149 

150 


CHAPTER   IX 
Reactions  of  Infusoria  to  the  Electric  Current 

1.  Diverse  Reactions  of  Different  Species  of  Infusoria 151 

A.  Reaction  to  Inductiun  Shocks     .         .         .         .         .         .         .         .         •I5I 

B.  Reaction  to  the  Constant  Current        ........  152 

2.  Summary           ..............  162 

3.  Theories  of  the  Reaction  to  Electricity 164 

Literature 169 


CHAPTER   X 

modifiability  of  behavior  in  infusoria,  and  behavior  under 
Natural  Conditions.    Food  Habits 

1.  Modifiability  of  Behavior  .         .         .         .         .         .         .         .         .         .         .170 

2.  The  Behavior  of  Infusoria  under  Natural  Conditions 179 

3.  Food  Habits 182 

Literature 187 


PART   II 


BEHAVIOR    OF   THE  LOWER  METAZOA 


CHAPTER   XI 
Introduction  and  Behavior  of  Ccelenterata 

Introduction 188 

Behavior  of  Ccelenterata iSS 

1.  Action  System.     Spontaneous  Activities 1S9 

2.  Conditions  required  for  Retaining  a  Given  Position  :   Righting  Reactions,  etc.         .  192 

3.  General  Reaction  to  Intense  Stimuli 197 

4.  Localized  Reactions 198 

5.  The  Rejecting  Reaction  of  Sea  Anemones 202 

6.  Locomotor  Reactions  in  Hydra  and  Sea  Anemones 203 


Xll  CONTENTS 

PAGE 

7.  Acclimatization  to  Stimuli 207 

8.  Reactions  to  Certain  Classes  of  Stimuli  ..........  208 

A.  Reactions  to  Electricity       ..........  208 

B.  Reactions  to  Gravity  ...........  210 

C.  Reactions  to  Light      ...........  212 

9.  Behavior  of  Ccelenterates  with  Relation  to  Food   .......  216 

A.  Food  and  Respiratory  Reactions  in  Hydra  .         .         .         .         .         .216 

B.  Food  Reactions  in  Medusas         .........  219 

C.  Food  Reactions  in  Sea  Anemones       .         .         .         .         .         .         .         .221 

10.  Independence  and  Correlation  of  Behavior  of  Different  Parts  of  the  Body    .         .  227 

11.  Some  General  Features  of  Behavior  in  Ccelenterates 230 

Literature 232 

CHAPTER   XII 

General  Features  of  Behavior  in  Other  Lower  Metazoa 

1.  Definite  Reaction  Forms  ("  Reflexes  ") 233 

2.  Reaction  by  Varied  Movements,  with  Selection  from  the  Resulting  Conditions        .  238 

3.  Modifiability  of  Behavior  and  its  Dependence  on  Physiological  States     .         .         .  250 
Literature 259 


PART    III 

ANALYSIS   OF  BEHAVIOR  IN  LOWER    ORGANISMS,    WITH  A 
DISCUSSION  OF  THEORIES 

CHAPTER   XIII 
Comparison  of  the  Behavior  of  Unicellular  and  Multicellular  Organisms    260 

CHAPTER   XIV 
Tropisms  and  the  Local  Action  Theory  of  Tropisms 265 

CHAPTER   XV 
Is  the  Behavior  of  the  Lower  Organisms  composed  of  Reflexes?         .        .    277 

CHAPTER  XVI 
Analysis  of  Behavior  in  Lower  Organisms 

Introductory 283 

1.     The  Causes  and  Determining  Factors  of  Movements  and  Reactions    .         .         .  2S3 

A.     The  Internal  Factors 283 

(1)  Activity  does  not  require  Present  External  Stimulation       .         .  283 

(2)  Activity  may  change  without  External  Cause       ....  285 

(3)  Changes  in  Activity  depend  on  Changes  in  Physiological  States  .  286 


CONTENTS  xiii 

PAGE 

(4)  Reactions  to  External  Agents  depend  on  Physiological  States     .  286 

(5)  The  Physiological  State  may  be  changed  by  Progressive  Internal 

Processes    ..........  287 

(6)  The    Physiological    State   may  be   changed    by   the  Action   of 

External  Agents          ........  287 

(7)  The  Physiological  State  may  be  changed  by  the  Activity  of  the 

Organism   ..........  288 

(8)  External  Agents  cause  Reaction  by  changing  the  Physiological 

State  of  the  Organism 288 

(9)  The  Behavior  of  the  Organism  at  any  Moment  depends  upon  its 

Physiological  State  at  that  Moment 288 

(10)  Physiological  States  change  in  Accordance  with  Certain  Laws    .  289 

(11)  Different  Factors  on  which  Behavior  Depends    ....  292 


CHAPTER   XVII 

Analysis  of  Behavior  (continued) 

B.     The  External  Factors  in  Behavior 293 

(1)  Relation  to  Physiological  States 293 

(2)  Change  of  Conditions  as  a  Cause  of  Reaction     ....  293 

(3)  Reaction  without  External  Change      ......  296 

(4)  Reactions  to  Representative  Stimuli    ......  296 

(5)  Relation  of  Reaction  to  Internal  Processes          ....  298 

(6)  Summary  of  the  External  Factors  which  produce  or  determine 

Reactions 299 

CHAPTER   XVIII 

Analysis  of  Behavior  (continued) 

2.  The  Nature  of  the  Movements  and  Reactions 300 

A.  The  Action  System 300 

B.  Negative  Reactions     ...........  301 

C.  Selection  from  the  Conditions  produced  by  Varied  Movements  .         .         .  302 

D.  "  Discrimination " 304 

E.  Adaptiveness  of  Movements        .........  305 

F.  Localization  of  Reactions    ..........  306 

G.  Positive  Reactions 309 

3.  Resume  of  the  Fundamental  Features  of  Behavior .312 

CHAPTER   XIX 

Development  of  Behavior 314 

CHAPTER  XX 

Relation  of  Behavior  in  Lower  Organisms  to  Psychic  Behavior    .        .        .  328 


xiv  CONTENTS 

CHAPTER    XXI 

Behavior  as  Regulation,  and  Regulation  in  Other  Fields 

PAGE 

1.  Introductory    ..............  338 

2.  Regulation  in  Behavior    ............  338 

A.     Factors  in  Regulation  in  the  Behavior  of  Lower  Organisms         .         .         .  339 

3.  Regulation  in  Other  Fields 345 

4.  Summary 349 

BIBLIOGRAPHY 351 

INDEX 359 


BEHAVIOR   OF    THE    LOWER   ORGANISMS 


PART    I 


THE   BEHAVIOR   OF   UNICELLULAR   ORGANISMS 


CHAPTER   I 

THE   BEHAVIOR   OF   AMCEBA 

i.   Structure  and  Movements  of  Amoeba 

The  typical  Amoeba  (Fig.  i)  is  a  shapeless  bit  of  jelly  like  protoplasm, 
continually  changing  as  it  moves  about  at  the  bottom  of  a  pool  amid 
the  debris  of  decayed  vegetation.  From  the  main  protoplasmic  mass 
there  are  sent  out,  usually  in  the  direction  of  locomotion,  a  number  of 


Fig.  i.  —  Amceba  proteus,  after  Leidy  (1879)  (slightly  modified),     c.v.,  contractile  vacuole; 
ec,  ectosarc;   en.,  endosarc;   nu.,  nucleus;  ps.,  pseudopodia. 


lobelike  or  pointed  projections,  the  pseudopodia  (Fig.  1,  ps.).  These 
are  withdrawn  at  intervals  and  replaced  by  others.  Within  the  mass 
of  protoplasm  certain  differentiations  are  observable.  Covering  the 
outer  surface  there  is  usually,  though  not  always,  a  transparent  layer 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


containing  no  granules;  this  is  called  the  ectosarc  (Fig.  i,  ec).  Within 
this  the  protoplasm  is  granular,  and  contains  bits  of  substance  taken  as 
food,  vacuoles  filled  with  water,  and  certain  other  structures.      This 

granular  protoplasm  is  known  as  the 
endosarc  (Fig.  i,  en.).  Within  the 
fluidlike  endosarc  we  find  two  well- 
defined  structures.  One  is  a  disk- 
like    or   rounded,   more  solid  body, 

Fig.  2. — Amoeba  Umax,  after  Leidy  (1870).     1  ,1  i  ,-•-.•  •> 

j  v    ivj    knoWn  as  the  nucleus  (Fig.  i,  nu.). 

The  other  is  a  spherical  globule  of  water,  which  at  intervals  collapses, 

emptying  the  contained  water  to  the  outside.     This  is  the  contractile 

vacuole  (Fig.  i,  c.v.). 

There  are  many  different  kinds  of  Amoebae,  varying  in  their  appear- 
ance and  structure.     For  our  purposes  it  will  be  sufficient  to  distinguish 

three  main  types.     In  one  type  the  form  is  very 

irregular  and   changeable,   and    there    are    many 

pseudopodia.      Of  this  type  Amceba  proteus  (Fig. 

1)  is  the  commonest    species.     In  a  second  type 

the  animal   usually   moves  forward  rapidly  as  a 

single  elongated  mass,  the  protoplasm  seeming  very 

fluid.     Amceba  Umax  (Fig.  2)  is  a  representative 

of  this   group.      A  third  type  consists  of  slowly 

moving  Amcebae,  of  nearly  constant  form,  usually  having  wrinkles  on  the 

surface,  and  with  the  thick  ectosarc  much  stiffened,  so  that  it  does  not 

appear  fluid  in  character.     The  commonest  representative  of  this  type 

is  Amceba  verrucosa  (Fig.  3). 

In  its  usual  locomotion  the  movement  of  Amoeba  is  in  many  respects 

comparable  to  rolling,  the  upper  surface  continually  passing  forward 

and  rolling  under  at  the  anterior  end,  so  as  to 
form  the  lower  surface.  This  may  best  be 
seen  by  mingling  soot  with  water  containing 
many  Amcebae.  Fine  granules  of  soot  cling 
readily  to  the  surface  of  Amcebae  of  the  verru- 
cosa type,  and  more  rarely  to  Amcebae  of  other 
types.  Such  particles  which  are  clinging  to 
the  upper  surface  move  steadily  forward  till 
they  reach  the  anterior  edge.  Here  they  are 
rolled  over  and  come  in  contact  with  the  sub- 
stratum. They  then  remain  quiet  till  the 
Amceba  has  passed  across  them.  Then  they 
pass  upward  again  at  the  posterior  end,  and 

This 


Fig.  3.  —  A  mceba  verru- 
cosa, after  Leidy  (1879). 


Fig.  4.  —  Paths  of  two  par- 
ticles attached  to  the  outer  sur- 
face of  Amoeba.  That  portion 
of  the  paths  that  is  on  the  lower 
surface  is  represented  by  broken 
lines.  The  two  particles  were 
seen  to  complete  the  circuit  of 
the  animal  five  or  six  times  in 
the  paths  shown.  (The  Amceba 
was  of  course  progressing;  no 
attempt  is  made  to  represent 
this  in  the  figure.) 


forward  once  more  to  the  anterior  edge. 


THE  BEHAVIOR   OF  AMCEBA  3 

is  repeated  as  long  as  the  particles  cling  to  the  surface.  Single  particles 
have  been  seen  to  pass  thus  many  times  around  the  body  of  the  animal. 
Diagrams  of  the  movements  of  the  particles  clinging  to  the  surface  are 
shown  in  Figs.  4  and  5. 

It  is  not  only  the  outermost  layer  of  the  ectosarc  that  thus  moves 
forward.     On  the  contrary,  the  whole  substance  of  the  Amoeba,  from  the 


Fig.  5.  —  Diagram  of  the  movements  of  a  particle  attached  to  the  outer  surface  of  Amceba 
verrucosa,  in  side  view.  In  position  1  the  particle  is  at  the  posterior  end;  as  the  Amceba  pro- 
gresses, it  moves  forward,  as  shown  at  2,  and  when  the  Amoeba  has  reached  the  position  3,  the 
particle  is  at  its  anterior  edge,  at  x.  Here  it  is  rolled  under  and  remains  in  position,  so  that 
when  the  Amceba  has  reached  the  position  4,  the  particle  is  still  at  x,  at  the  middle  of  its  lower 
surface.  In  position  5  the  particle  is  still  at  the  same  place  x,  save  that  it  is  lifted  upward 
a  little  as  the  posterior  end  of  the  animal  becomes  free  from  the  substratum.  Now  as  the  Amceba 
passes  forward,  the  particle  is  carried  to  the  upper  surface,  as  shown  at  6.  Thence  it  continues 
forward,  and  again  passes  beneath  the  Amceba. 

outer  surface  to  the  interior  of  the  endosarc,  moves  steadily  forward 
as  a  single  stream,  only  the  part  in  contact  with  the  substratum  being  at 
rest.  At  times  small  particles  are  at  first  attached  to  the  outer  surface, 
then  gradually  sink  through  the  ectosarc  into  the  endosarc.  Through- 
out the  entire  process  of  sinking  inward  the  movement  is  steadily  for- 
ward. 

It  is  clear,  then,  that  Amceba  rolls,  the  upper  surface  continually  pass- 
ing across  the  anterior  end  to  form  the  lower  surface.  The  anterior 
edge  is  thin  and  flat  and  is  attached  to  the  substratum,  while  the  posterior 


Fig.  6.  —  Diagram  of  the  movements  in  a  progressing  Amceba  in  side  view.  A,. anterior 
end;  P,  posterior  end.  The  large  arrow  above  shows  the  direction  of  locomotion:  the  other 
arrows  show  the  direction  of  the  protoplasmic  currents,  the  longer  ones  representing  more  rapid 
currents.  From  a  to  x  the  surface  is  attached  and  at  rest.  From  x  to  y  the  protoplasm  is  not 
attached  and  is  slowly  contracting,  on  the  lower  surface  as  well  as  above,  a,  b,  c,  successive 
positions  occupied  by  the  anterior  edge.  As  the  animal  rolls  forward,  it  comes  later  to  occupy 
the  position  shown  by  the  broken  outline. 


end  is  high  and  rounded,  and  is  not  attached  to  the  substratum.     A 
very  good  idea  of  the  character  of  the  movements  of  Amceba  may  be 


4  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

obtained  in  the  following  way:  Pin  two  edges  of  a  handkerchief  to- 
gether, so  as  to  make  a  flat  cylinder.  Within  this  place  some  heavy 
objects  that  will  fill  part  of  the  cylinder,  and  lay  the  whole  on  a  flat  sur- 
face. Now  pull  forward  the  upper  surface  of  the  cloth  near  the  anterior 
edge,  a  little  at  a  time,  bringing  it  in  contact  with  the  substratum.  If 
this  process  is  continued,  the  handkerchief  rolls  slowly  forward  with  thin 
anterior  edge  and  high  posterior  portion,  —  the  weight  within  dragging 
behind.  The  lower  surface  is  at  rest  while  the  upper  surface  moves 
forward.  In  all  these  respects  the  movement  is  like  the  locomotion  of 
Amoeba.  A  diagram  of  the  movement  of  Amceba  as  it  would  appear 
in  side  view  is  given  in  Fig.  6. 

While  typically  all  the  currents  are  forward  in  a  progressing  Amoeba, 
any  portion  of  the  protoplasm  may  be  excluded  temporarily  from  the 
currents.  This  is  especially  common  at  the  posterior  end  or  tail,  which 
is  often  composed  of  quiet  protoplasm,  covered  with  wrinkles  or  papillae 
But  the  substance  of  the  tail  is  in  the  course  of  time  drawn  into  the  cur- 
rents and  passes  forward. 

In  the  formation  of  pseudopodia  the  movement  is  much  like  that  at 
the  anterior  end  of  the  body.  If  the  pseudopodium  is  in  contact  with  the 
substratum,  the  upper  surface  moves  forward  while  the  lower  surface  is 
at  rest.  If  the  pseudopodium  is  sent  forth  freely  into  the  water,  its 
entire  surface  moves  outward,  in  the  same  direction  as  the  tip.  These 
movements  have  been  determined  by  observing  the  motion  of  particles 
attached  to  the  outer  surface  of  extending  pseudopodia. 

In  some  Amoebae,  according  to  Rhumbler  (1898,  1905),  the  external 
protoplasmic  currents  turn  backward  at  the  sides  of  the  anterior  end, 
so  that  there  is  produced  a  fountainlike  arrangement,  an  internal 
current  forward,  external  currents  backward.  Such  currents  resemble 
those  due  to  local  decrease  of  surface  tension  in  a  drop  of  inorganic  fluid. 

Through  such  a  local 
decrease  the  tension 

/^_  „ -  * —  -^~  ■« — *j\  p     or  pulling  along  the 

surface  is  lessened 
in  a  given  region, 
so  that  the  remain- 

FiG.  7.  —  Currents  in  a  drop  of  fluid  when  the  surface  tension  .  -      .  . 

is  decreased  on  one  side.     A,  the  currents  in  a  suspended  drop,  OCT     OI     tne    SUTiace 

when  the  surface  tension  is  decreased  at  a.     After  Berthold.      B,  fllni   is   Dulling  more 
axial  and  surface  currents  in  a  drop  of  clove  oh  in  which  the  ,  .    '     , 

surface  tension  is  decreased  at  the  side  a.     The  drop  elongates  Strong!)  ,      It     tnere- 

and  moves  in   the  direction  of  a,  so  that  an  anterior  (a)  and  a  fore    dl'a^S    the    SUT- 

posterior  (p)  end  are  distinguishable.  {  ]  (     +1 

drop  away  from  the  point  of  lowered  tension.     The  result  is  that  cur- 
rents pass  on  the  surface  in  all  directions  away  from  this  point  (Fig.  7). 


THE   BEHAVIOR   OF   AMCEBA 


At  the  same  time  the  inward  pressure  is  decreased  in  the  region  of 
lowered  tension,  while  elsewhere  the  pressure  remains  the  same.  Hence 
the  internal  fluid  of  the  drop  is  pressed  out  toward  the  region  where  the 
film  is  weakened ;  a  current  flows  in  the  central  part  of  the  drop  toward 
this  point.  This  current  may  produce  a  projection  at  the  point  of 
lowered  tension,  provided  the  surface  currents  do  not  carry  the  fluid  back 
as  fast  as  it  is  brought  forward. 

It  was  long  supposed  that  the  movements  of  all  sorts  of  Amoebae 
were  of  this  character.  As  a  natural  conclusion,  it  was  commonly  held 
that  locomotion  and  the  formation  of  pseudopodia  in  Amoeba  are  due 
to  a  local  decrease  in  surface  tension  at  the  region  of  forward  move- 
ment. As  our  account  shows,  most  Amoebae  do  not  move  at  all  as  do 
liquid  drops  whose  movements  are  produced  through  changes  in  surface 
tension.1  Rolling  movements  with  all  currents  forward  cannot  be  pro- 
duced experimentally  through  local  changes  in  the  surface  tension  of  a 
drop  of  fluid.  It  is  necessary,  therefore,  to  abandon  the  surface  tension 
theory  for  those  Amoebae  that  move  in  the  way  shown  in  Fig.  6.  If  the 
theory  is  still  maintained  for  the  Amoebae  with  backward  currents,  this 
involves  holding  that  the  movements  are  due  to  fundamentally  dif- 
ferent causes  in  different  Amoebae  ;  this  is  the  view  maintained  by 
Rhumbler  (1905). 

While  most  Amoebae  roll  as  they  progress,  different  species  differ  greatly 
in  special  features  of  their  movements.  The  species  of  the  verrucosa 
type  (Fig.  3)  move  slowly  and  change 
form  very  little,  not  sending  out 
pseudopodia.  Those  of  the  Umax 
type  (Fig.  2)  move  more  rapidly  and 
change  form  more  frequently,  but  they 
rarely  send  out  pseudopodia.  Finally, 
in  the  proteus  type  (Fig.  1)  the  form 
is  excessively  changeable,  many  pseu- 
dopodia extending  and  retracting. 
Many  Amoebae  show  what  might  be 
called  specialized  habits  in  their  usual 
movements.  For  example,  Amoeba  angulata  and  Amoeba  velata  usually 
send  forth  at  the  anterior  edge  a  pseudopodium  which  extends  freely  into 
the  water  and  waves  back  and   forth,  serving  as  a  feeler  or  antenna 


Fig.  8. — Amwba  velata,  showing  the 
antennalike  anterior  pseudopodium  pro- 
jecting freely  into  the  water.  After 
Penard  (1902). 


1  According  to  Rhumbler  (1905),  such  movements  are  most  readily  seen  in  a  species  of 
Amoeba  living  parasitically  in  the  intestine  of  the  cockroach.  Whether  the  currents  on  the 
upper  surface  are  actually  backward,  where  the  interior  currents  are  forward,  as  is  required 
if  the  movements  are  to  be  explained  by  local  decrease  of  surface  tension,  has  not  been 
shown. 


6  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

(Fig.  8).     Many  other  special  peculiarities  of  movement  are  described 
in  the  great  work  of  Penard  (1902)  on  these  organisms. 

2.   Reactions  of  Amceba  to  Stimuli 

The  conditions  under  which  Amceba  lives  are  not  always  the  same, 
and  as  the  conditions  change,  the  behavior  of  Amceba  changes  also. 
Such  changes  in  behavior  are  usually  called  reactions,  while  the  external 
agents  that  induce  them  are  called  stimuli. 


A.   Reaction  to  Contact  with  Solids 

One  of  the  commonest  stimuli  is  that  due  to  contact  with  a  solid 
object.     If  a  solid  body  strikes  strongly  against  one  side  or  one  end  of  a 

moving  Amceba,  the  part  affected  contracts 
and  releases  its  hold  on  the  substratum, 
and  the  internal  currents  start  away  from 
it.  The  Amceba  changes  its  course  and 
moves  in  another  direction.  We  may  call 
this  a  negative  reaction,  since  it  takes  the 
animal  away  from  the  source  of  stimulation. 
This  reaction  can  be  produced  experi- 
mentally by  touching  the  animal,  under  the 
microscope,  with  the  tip  of  a  glass  rod 
drawn  to  a  minute  point  (Fig.  9).  The 
animal  does  not,  as  a  rule,  move  directly 
away  from  the  side  touched,  but  merely  in 
some  other  direction  than  toward  this  side. 
If  we  touch  it  at  the  anterior  edge,  the  part 
touched  stops  and  contracts,  while  the  cur- 
rent turns  to  one  side  at  this  point,  so  that 
the  animal  moves  at  an  angle  with  its  for- 
mer course  (Fig.  9).  Often  the  course  is 
altered  only  a  little  in  this  way.  But  if  all  of  one  side  or  one  end  is 
strongly  stimulated,  then  a  pseudopodium  may  be  sent  out  on  the  side 
opposite,  so  that  the  animal  moves  almost  directly  away  from  the  stimu- 
lated region  (Fig.  10). 

By  repeatedly  stimulating  Amceba  it  is  possible  to  drive  it  in  any 
desired  direction.  The  advancing  edge  is  touched  with  the  rod ;  it 
thereupon  withdraws.  A  new  pseudopodium  is  sent  out  elsewhere. 
If  this  does  not  lead  in  the  direction  desired,  it  is  touched,  causing  retrac- 
tion,  whereupon  the  Amceba  tries  a  new  direction.     This  continues 


Fig.  q.  —  Negative  reaction  to 
mechanical  stimulation  in  Amceba. 
An  Amceba  advancing  in  the  direc- 
tion shown  by  the  arrows  is  stimu- 
lated with  the  tip  of  a  glass  rod  at 
its  anterior  edge  (a).  Thereupon 
this  part  is  contracted,  the  currents 
are  changed,  and  a  new  pseudo- 
podium sent  out  (&). 


THE  BEHAVIOR   OF  AMCEBA 


till  a  pseudopodium  is  sent  out  in  the  direction  desired  by  the  experi- 
menter. The  animal  may  now  be  compelled  to  follow  a  definite  straight 
course,  by  stimulating  any  pseudopodium 
which  tends  to  diverge  from  this  course. 

If  the  posterior  end  of  a  moving 
Amoeba  is  stimulated,  the  animal  con-  & 
tinues  to  move  forward,  usually  hastening 
its  course  a  little.  The  posterior  end  is 
of  course  already  contracted,  and  the 
new  stimulation  merely  causes  it  to  con- 
tract a  little  more. 

The  negative  reaction  is  of  course 
the  method  by  which  Amoeba  avoids 
obstacles.  If  an  Amoeba  in  creeping 
comes  against  a  small   solid   bodv,   the 

, .        .       j.         ,  ,  i       i    r        i     i  Fig.  io.  —  Negative  reaction  to  a 

reaction  is  often  less  sharply  defined  than    mechamcai  stimulus  when  the  entire 

in     the     Cases     which    we     have     thus    far      anterior  end  is  strongly  stimulated,     a 
,  -i       i         a  -l  i       •        i  and  b,  successive  stages.     The  arrow 

described.     A  typical  example  is  shown    x  shows  the  original   direction  of 

in  Fig.  II.      A  progressing  Amoeba  Came      motion;    the    arrows    in    a    show    the 

.  .  .,,      '    .    .  .  currents  immediately  after  stimulation. 

in  contact  at  the  middle  of  its  anterior    In  b  a  new  taii  (/')  has  been  formed 

edge    With    the    end    Of    a    dead    alga    fila-      from  the  former  anterior  end,  uniting 
,-,-,1  ,T  ,  ,      with  the  old  tail  (/). 

ment.     1  hereupon  the  protoplasm  ceased 

to  flow  forward  at  the  point  of  contact  c,  while  on  each  side  of 
this  point  the  motion  continued  as  before.  In  a  short  time,  there- 
fore, the  animal  had  the  form  and  position  shown  by  the  broken 
outline  in  Fig.  1 1 ;  the  filament  projected  deeply  into  a  notch  at  the 
anterior  edge.  Motion  continued  in  this  manner  would  have  divided 
the  Amoeba  into  two  parts.  But  soon  motion  ceased  on  one  side  (x), 
while  it  continued  on  the  side  y.     The  currents  in  x  became  reversed 


x . 


Method  by  which  Amoeba  avoids  an  obstacle. 


and  flowed  around  the  end  of  the  filament  into  y,  as  shown  at  B,  Fig.  n. 
Thus  the  animal  had  avoided  the  obstacle  by  reversing  a  part  of  the 
current  and  flowing  in  another  direction. 

But  not  all  mechanical  stimuli  cause  a  negative  reaction.     Some- 


8 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


times  Amoeba,  on  coming  in  contact  with  a  solid  body,  turns  and  moves 
toward  it,  —  responding  thus  by  a  positive  reaction.  At  times  an 
Amoeba  which  is  moving  along  on  the  glass  slip  used  in  microscopic 
work  comes  in  contact  by  its  upper  surface  with  the  under  surface  of 
the  cover-glass.     Thereupon  it  sometimes  pushes  forth  a  pseudopodium 


Fig.  12.  —  Amceba  velata  passing  from  the  slide  to  the  cover-glass,  side  view.  After  Penard 
(1002).  At  a  the  animal  is  creeping  in  the  usual  way,  with  the  tentaclelike  pseudopodium 
projecting  into  the  water.  At  b  the  pseudopodium  has  reached  the  cover-glass  and  attached 
itself.    At  c  the  animal  has  released  its  hold  on  the  slide,  and  is  now  attached  to  the  cover  alone. 

on  this  under  surface;  the  pseudopodium  attaches  itself;  the  Amoeba 
releases  its  hold  on  the  slide,  and  now  continues  its  course  on  the  under 
side  of  the  cover-glass.  Penard  (1902)  has  observed  this  in  Amceba 
velata,  when  the  long,  tentaclelike  anterior  pseudopodium  of  this  ani- 
mal comes  during  its  feeling  movement  in  contact  with  the  cover-glass. 
The  process  is  represented  in  Fig.  12.  In  a  similar  manner  Amoebae 
frequently  pass  to  the  under  side  of  the  surface  film  of  water,  creeping 
on  this  as  if  it  were  a  solid  body. 

Under  certain  circumstances  Amceba  seems  especially  disposed 
toward  this  positive  reaction.     Sometimes  an  Amoeba  is  left  suspended 

in  the  water,  not  in  contact  with 
anything  solid.  Under  such  cir- 
cumstances the  animal  is  as  nearly 
completely  unstimulated  as  it  is 
possible  for  an  Amoeba  to  be ;  it 
is  contact  only  with  the  water, 
and  that  uniformly  on  all  sides.- 
But  such  a  condition  is  most  un- 
favorable for  its  normal  activities ; 
it  cannot  move  from  place  to 
place,  and  has  no  opportunity  to 
obtain  food.  Amoeba  has  a 
method  of  behavior  by  which  it 
meets  these  unfavorable  condi- 
tions. It  usually  sends  out  long, 
slender  pseudopodia  in  all  direc- 
tions, as  illustrated  in  Fig.  13. 
The  body  may  become  reduced  to  little  more  than  a  meeting  point  for 

It  is  evident  that  the  sending  out  of  these  long  arms 


Fig.  13. — Amoeba  proteus  suspended  in  the 
water,  showing  the  long  pseudopodia  extended 
in  all  directions.     After  Leidy  (1879). 


these  pseudopodia. 


THE  BEHAVIOR   OF  AMCEBA 


greatly  increases  the  chances  of  coming  in  contact  with  a  solid  body,  and 
it  is  equally  evident  that  contact  with  a  solid  is  under  the  circumstances 
exactly  what  will  be  most  advantageous  to  the  animal.  As  soon  as  the 
tip  of  one  of  the  pseudopodia  does  come  in  contact  with  something 
solid,  the  behavior  changes  (Fig.  14).     The  tip  of  the  pseudopodium 


~b  c 

Fig.  14.  —  Method  by  which  a  floating  Amoeba  passes  to  a  solid. 


spreads  out  on  the  surface  of  the  solid  and  clings  to  it.  Currents  of 
protoplasm  begin  to  flow  in  the  direction  of  the  attached  tip.  The 
other  pseudopodia  are  slowly  withdrawn  into  the  body,  while  the  body 
itself  passes  to  the  surface  of  the  solid.  After  a  short  time  the  Amoeba, 
which  had  been  composed  merely  of  a  number  of  long  arms  radiating 
in  all  directions  from  a  centre,  has  formed  a  collected  flat  mass,  creep- 
ing alone:  a  surface  in  the  usual  way.  This  entire  reaction  seems  a  re- 
markable  one  in  its  adaptiveness  to  the  peculiar  circumstances  under 
which  the  organism  has  been  placed. 

Positive  reactions  toward  solid  bodies  are  particularly  common  in 
the  process  of  obtaining  food.  In  our  account  of  the  food  reactions  we 
shall  give  examples  of  striking  and  long-continued  reactions  of  this  sort. 


B.    Reactions  to  Chemicals,  Heat,  Light,  and  Electricity 

Reactions  to  Chemicals.  —  If  a  strong  chemical  in  solution  diffuses 
against  one  side  or  end  of  the  body,  the  Amoeba  contracts  the  part  af- 
fected, releasing  it  from  the  substratum,  while  the  protoplasmic  cur- 
rents start  in  some  other  direction.  The  animal  has  thus  changed  its 
course.  The  reaction  to  chemicals  can  best  be  shown  in  the  following 
way.  The  tip  of  a  capillary  glass  rod  is  moistened,  then  dipped  in  some 
powdered  chemical,  preferably  a  colored  one,  such  as  methyline  blue. 
This  tip  is  then,  under  the  microscope,  brought  close  to  one  side  of  an 
Amoeba  in  an  uncovered  drop  of  water.  As  soon  as  the  diffusing 
chemical  comes  in  contact  with  one  side  of  the  body,  the  reaction  occurs. 
Chemicals  that  are  fluid  may  be  drawn  into  an  excessively  fine  capillary 
tube  and  the  tip  of  this  held  near  the  Amoeba.  Some  of  the  variations 
in  the  reactions  to  chemicals  are  shown  in  Fig.  15. 


10 


BEHAVIOR   OF   THE    LOWER   ORGANISMS 


Such  experiments  show  that  Amoeba  is  very  sensitive  to  changes  in 
the  chemical  composition  of  the  water  surrounding  it,  and  is  inclined 
to  move  away  whenever  it  comes  to  a  region  in  which  the  water  differs 
even  slightly  from  that  to  which  it  is  accustomed.  It  has  been  shown 
to  react  negatively  when  the  following  substances  come  in  contact  with 
one  side  of  its  body:  methyline  blue,  methyl  green,  sodium  chloride, 
sodium  carbonate,  potassium  nitrate,  potassium  hydroxide,  acetic  acid, 
hydrochloric  acid,  cane  sugar,  distilled  water,  tap  water,  and  water 


-O.'V 


a 

Fig.  15.  —  Variations  in  the  reactions  of  Amceba  to  chemicals.  The  dotted  area  represents 
in  each  case  the  diffusing  chemical.    The  arrows  show  the  direction  of  the  protoplasmic  currents. 

a.  A  little  methyl  green  diffuses  against  the  anterior  end  of  an  Amceba.  The  latter  reacts 
by  sending  out  a  new  pseudopodium  at  one  side  of  the  anterior  end  and  moving  in  the  direction 
so  indicated. 

b.  A  solution  of  NaC!  diffuses  against  the  right  side  of  a  moving  Amoeba  (1).  The  side 
affected  contracts  and  wrinkles  strongly,  while  the  opposite  side  spreads  out  (2),  the  currents 
flowing  as  shown  by  the  arrows. 

c.  A  solution  of  NaCl  diffuses  against  the  anterior  end  of  an  advancing  Amceba.  A  broad 
pseudopodium,  shown  by  the  dotted  outline,  pushes  out  from  the  posterior  region,  above  the  end, 
and  the  course  is  reversed. 

d.  A  solution  of  methyline  blue  diffuses  against  the  anterior  end  of  an  Amceba  (1).  There- 
upon a  pseudopodium  is  sent  out  on  each  side  of  the  posterior  end  at  right  angles  with  the  original 
course  (2).     Into  these  the  entire  substance  of  the  animal  is  drawn  (3). 


from  other  cultures  than  that  in  which  the  Amceba  under  experimen- 
tation lives. 

Reaction  to  Heat.  —  If  one  side  of  an  Amceba  is  heated,  it  reacts  in 
the  same  negative  way  as  to  chemicals  or  to  a  mechanical  shock.  The 
reaction  to  heat  may  be  observed  as  follows:  An  Amceba  creeping 
on  the  under  surface  of  the  cover-glass  is  chosen  for  the  experiment. 
The  point  of  a  needle  is  heated  in  a  flame  and  placed  against  the  cover- 
glass  in  front  of  the  Amceba,  or  a  little  to  one  side  of  it.  If  the  needle 
is  not  brought  too  close  so  as  to  affect  the  whole  body  instead  of  only 


THE  BEHAVIOR   OF  AMCEBA 


II 


d        one  side,  the  animal  responds  by 
cs     7?  10  contracting  the  part  affected  and 

moving  in  some  other  direction. 
Reactions  to  Light.  —  Light  has  a  peculiar 
effect  on  Amoeba.     In  general  its  functions 
seem  better  performed  in  the  dark;  strong 
light  interferes  with  them  seriously.    Rhum- 
bler  (1898)   observed   that   if  Amoebae  are 
suddenly  subjected  to  light  while  busy  feed- 
ing on  Oscillaria   filaments,   they  cease  to 
feed,  and   even  give  out   the   partly  ingested  filaments. 
Harrington   and   Learning   (1900)   found    that    ordinary 
white  light  thrown  on  a  moving  Amoeba  causes  it    to 
come  to  rest  at  once.     Blue  light  acts  in  the  same  way, 
while  in  red  light  the  movements  are  as  free  as  in  dark- 
ness.   Other  colors  have  intermediate  effects.    Engelmann 
(1879)  found  that  sudden  illumination  causes  an  extended 
Pelomyxa  (which  is  merely  a  very  large  Amoeba)  to  con- 
tract suddenly.    It  is  well  known  that  exposure  to  strong 
light  is  destructive  to  most  lower  organisms. 

In  correspondence  with  the  fact  that  light  interferes 
with  its  activities,  we  find  that  Amoeba  moves  away  from 
a  source  of  strong  light.     If  the  sun  is  allowed  to  shine 
on  it  from  one  side,  it  moves,  as  Davenport  (1897)  shows, 
in  the  opposite  direction.     It  thus  moves  in  a  general 
way  in  the  same  direction  as  the  rays  of 
light  (Fig.  16).     It  is  a  peculiar  fact  that 
experiments    so    far   have   not    shown    a 
negative  reaction  to  occur  when  light  is 
thrown  from  directly  above  or  below  on 
one  side  or  end  of  an  Amoeba.     The  fact 
that  the  whole  body  contracts  when  illumi- 
nated, as  shown  by  the  work  of  Engel- 

shown    by    the    arrow  a    was    then  -  1111 

thrown  upon  it.     it  changed  its    mann  (1879)  on  Pelomyxa,  would  lead  us 
course,  occupying  successively  the    to  expect  that  when  a  portion  of  the  body 

is  illuminated,  this  would  contract,  pro- 
ducing thus  a  negative  reaction.    But  this 


h 


Fig.  16. —  Reaction  of  Amoeba 
to  light,  after  Davenport  (1897). 
The  Amoeba  was  first  moving  in  the 
direction  indicated  by  the  arrow  x. 
Light    coming    from    the    direction 


positions  1,  2,  3,  4.  The  direction  of 
the  light  was  successively  changed  as 
indicated  by  the  arrows  b,  c,  d;  the 
numbers  5-14  show  the  successive 
positions  occupied  by  the  animal.  It 
will  be  observed  that  in  every  case  as 
soon  as  the  direction  of  the  light  is 
changed,  the  Amoeba  changes  its 
course  in  a  corresponding  way,  so  as 
to  retreat  steadily  from  the  source  of 
light. 


has  not  been  demonstrated.  The  experi- 
mental difficulties  are  great,  and  this  may 
account  for  the  lack  of  positive  results. 
If  future  work  substantiates  the  fact  that 
fight  falling  obliquely  on  one  side  causes 


12 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


a  reaction,  while  light  falling  from  above  or  below  on  one  side  causes 
none,  this  would  seem  to  indicate  that  the  direction  of  the  rays  in 
passing  through  the  body  has  something  to  do  with  determining  the 
direction  of  locomotion.  But  in  the  myxomycete  plasmodium,  which 
resembles  Amoeba  in  its  movements  and  in  many  other  respects,  light 
falling  from  above  or  below  on  a  part  of  the  body  does  produce  a 
negative  reaction,  —  the  withdrawal  of  the  part  affected.  Probably 
further  experimentation  will  show  the  same  thing  to  be  true  in  Amoeba. 
Reaction  to  Electricity.  —  Electric  currents  probably  form  no  part  of 
the  normal  environment  of  Amoeba,  yet  the  animal  reacts  in  a  very  defi- 
nite way  when  a  continuous  current  is  passed  through  the  water  con- 
taining it.  That  side  of  the  body  which  is  directed  toward  the  positive 
pole  or  anode  contracts  as  if  the  animal  were  strongly  stimulated 
here.    Then  a  pseudopodium  starts  out  somewhere  on  the  side  directed 


+ 


Fig.  17.  —  Reaction  of  Amoeba  to  the  electric  current.  The  arrows  show  the  direction  of 
the  protoplasmic  currents;  at  1  the  direction  of  movement  before  the  current  acts  is  shown. 
2,  3,  4,  successive  positions  after  the  current  is  passed  through  the  preparation. 


toward  the  negative  pole  or  cathode,  and  the  Amoeba  creeps  in  that  direc- 
tion (Fig.  17).  The  reaction  takes  place  throughout  as  if  the  Amoeba 
were  strongly  stimulated  on  the  anode  side.  If  the  electric  current  is 
made  very  strong,  the  anode  side  contracts  still  more  powerfully,  and 
the  Amoeba  bursts  open  on  the  opposite  side.  The  current  is  thus  very 
injurious. 

C.    How  Amoeba  gets  Food 

In  the  water  in  which  Amoeba  lives  are  found  many  other  minute 
animals  and  plants.  Upon  these  Amoeba  preys,  taking  indifferently  an 
animal  or  a  vegetable  diet.  Its  behavior  while  engaged  in  obtaining 
food  is  very  remarkable  for  so  simple  an  animal. 

Spherical  cysts  of  Euglena  are  a  common  food  with  Amceba  proleus. 
These  cysts  are  smooth  and  spherical,  easily  rolling  when  touched,  so 
that  they  present  considerable  difficulties  to  an  Amoeba  attempting  to 


THE  BEHAVIOR   OF   AMCEBA 


13 


ingest  them.  One  or  two  concrete  cases  will  illustrate  the  behavior  of 
Amoeba  when  presented  with  the  problem  of  obtaining  such  an  object 
as  food. 

A  spherical  Euglena  cyst  lay  in  the  path  of  an  advancing  Amceba 
proteus.  The  latter  came  against  the  cyst  and  pushed  it  ahead  a  short 
distance.  The  cyst  did  not  cling  to  the  protoplasm,  but  rolled  away 
as  soon  as  it  was  touched,  and  this  rolling  away  continued  as  long  as  the 
animal  moved  forward.  Now  that  part  of  the  Amceba  that  was  imme- 
diately behind  the  cyst  stopped  moving,  so  that  the  cyst  was  no  longer 
pushed  forward.  At  the  same  time  a  pseudopodium  was  sent  out  on 
each  side  of  the  cyst  (Fig.  18),  so  that  the  latter  was  enclosed  in  a  little 
bay.  Meanwhile,  a  thin  sheet  of  protoplasm  passed  from  the  upper 
surface  of  the  Amceba 
over  the  cyst  (Fig. 
18,  2).  The  two  lat- 
eral pseudopodia  be- 
came bent  together  at 
their  free  ends;  the 
cyst  was  thus  held  so 
that  it  could  not  roll 
away.  The  pseudo- 
podia and  the  over- 
lying sheet  of  proto- 
plasm fused  at  their  Fig.  18. 
free  ends,  so  that  the 

cyst  was  completely  enclosed,  together  with  a  quantity  of  water 
was  then  carried  away  .by  the  animal. 

Amceba  does  not  always  succeed  in  obtaining  its  food  so  easily  as 
in  the  case  described.  Often  the  cyst  rolls  away  so  lightly  that  the 
animal  fails  to  grasp  and  enclose  it.  In  such  a  case  Amceba  may  con- 
tinue its  efforts  a  long  time. 

Thus,  in  a  case  observed  by  the  author,  an  Amoeba  proteus  was  mov- 
ing toward  a  Euglena  cyst  (Fig.  19).  When  the  anterior  edge  of  the 
Amceba  came  in  contact  with  it,  the  cyst  rolled  forward  a  little  and 
slipped  to  the  left.  The  Amoeba  followed.  When  it  reached  the  cyst 
again,  the  latter  was  again  pushed  forward  and  to  the  left.  The  Amceba 
continued  to  follow.  This  process  was  continued  till  the  two  had  trav- 
ersed about  one-fourth  the  circumference  of  a  circle.  Then  (at  3)  the 
cyst  when  pushed  forward  rolled  to  the  left,  quite  out  of  contact  with 
the  animal.  The  latter  then  continued  straight  forward,  with  broad 
anterior  edge,  in  a  direction  which  would  have  taken  it  away  from  the 
food.     But  a  small  pseudopodium  on  the  left  side  came  in  contact  with 


■  Amoeba  ingesting  a  Euglena  cyst. 
sive  stages  in  the  process. 


1,  2,  3,  4,  succes- 


It 


14 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


the  cyst,  whereupon  the  Amoeba  turned  and  again  followed  the  rolling 
ball.  At  times  the  animal  sent  out  two  pseudopodia,  one  on  each  side 
the  cyst  (as  at  4),  as  if  trying  to  enclose  the  latter,  but  the  spherical  cyst 
rolled  so  easily  that  this  did  not  succeed.  At  other  times  a  single,  long, 
slender  pseudopodium  was  sent  out,  only  its  tip  remaining  in  contact 
with  the  cyst  (Fig.  19,  5);  then  the  body  was  brought  up  from  the  rear, 
and  the  food  pushed  farther.  Thus  the  chase  continued  until  the  roll- 
ing cyst  and  the  following  Amceba  had  described  almost  a  complete 


Fig.  19. —  Amoeba  following  a  rolling  Euglena  cyst.      The  figures  1-9  show  successive 

positions  occupied  by  Amceba  and  cyst. 


circle,  returning  nearly  to  the  point  where  the  Amceba  had  first  come 
in  contact  with  the  cyst.  At  this  point  the  cyst  rolled  to  the  right  as  it 
was  pushed  forward  (7).  The  Amceba  followed  (8,  9).  This  new  path 
was  continued  for  some  time.  The  direction  in  which  the  ball  was 
rolling  would  soon  have  brought  it  against  an  obstacle,  so  that  it  seemed 
probable  that  the  Amceba  would  finally  secure  it.  But  at  this  point, 
after  the  chase  had  lasted  ten  or  fifteen  minutes,  a  ciliate  infusorian 
whisked  the  ball  away  in  its  ciliary  vortex. 

Such  behavior  makes  a  striking  impression  on  the  observer  who 


THE  BEHAVIOR   OF  AMCEBA 


15 


sees  it  for  the  first  time.  The  Amoeba  conducts  itself  in  its  efforts  to 
obtain  food  in  much  the  same  way  as  animals  far  higher  in  the  scale. 
In  cultures  containing  many  Amcebae  and  many  Euglena  cysts  it  is  not 
at  all  rare  to  find  specimens  thus  engaged  in  following  a  rolling  ball  of 
food.     Sometimes  the  chase  is  finally  successful;    sometimes  it  Is  not. 

Many  of  the  cysts  are  attached  to  the  substratum.  Amceba  often 
attempts  to  take  such  cysts  as  food,  sending  pseudopodia  on  each  side 
of  and  above  them,  in  the  usual  way,  then  covering  them  completely 
with  its  body.     But  it  finally  gives  up  the  attempt  and  passes  on. 

Sometimes  when  a  single  pseudopodium  comes  in  contact  with  a 
cyst,  this  pseudopodium  alone  reacts,  stretching  out  and  pushing  the 
cyst  ahead  of  it  and  keeping  in  contact  with  it  as  long  as  possible.  Mean- 
while the  remainder  of  the  Amceba  moves  in  some  other  direction  (Fig. 
20).     Finally  the  pseudopodium  is  pulled  by  the  rest  of  the  body  away 


Fig.  20.  —  A  single  pseudopodium  (.v)  reacts  positively  to  a  Euglena  cyst,  its  protoplasm 
flowing  in  the  direction  of  the  cyst  and  pushing  it  forward,  while  the  remainder  of  the  Amceba 
moves  in  another  direction.  1-4,  successive  forms  taken.  At  4  the  reacting  pseudopodium 
is  pulled  away  from  the  cyst,  whereupon  it  contracts. 


from  the  cyst.  Again,  two  pseudopodia  on  opposite  sides  of  the  body 
may  each  come  in  contact  with  a  cyst.  Each  then  stretches  out,  pull- 
ing a  portion  of  the  body  with  it,  and  follows  its  cyst.  Soon  the  body 
comes  to  form  two  halves  connected  only  by  a  narrow  isthmus.  Finally 
one  half  succeeds  in  pulling  the  other  away  from  its  attachment  to  the 
bottom.  The  latter,  half  then  contracts*  and  the  entire  Amceba  follows 
the  victorious  pseudopodium. 

Amcebae  frequently  prey  upon  each  other.  Sometimes  the  prey  is 
contracted  and  does  not  move;  then  there  is  no  difficulty  in  ingesting 
it.  Such  a  case  has  been  described  and  figured  by  Leidy  (1879,  p.  94, 
and  PI.  7,  Figs.  12-19).  But  the  victim  does  not  always  conduct  itself 
so  passively  as  in  this  case,  and  sometimes  finally  escapes  from  its 
pursuer.  This  may  be  illustrated  by  a  case  observed  by  the  present 
writer  (Fig.  21). 


i6 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


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THE  BEHAVIOR   OF   AMCEBA  17 

I  had  attempted  to  cut  an  Amoeba  in  two  with  the  tip  of  a  fine  glass 
rod.  The  posterior  third  of  the  animal,  in  the  form  of  a  wrinkled  ball, 
remained  attached  to  the  rest  of  the  body  by  only  a  slender  cord,  — 
the  remains  of  the  ectosarc.  The  Amoeba  began  to  creep  away,  drag- 
ging with  it  this  ball.  This  Amoeba  may  be  called  a,  while  the  ball 
will  be  designated  b  (see  Fig.  21).  A  larger  Amoeba  (c)  approached, 
moving  at  right  angles  to  the  path  of  the  first  specimen.  Its  path  acci- 
dentally brought  it  in  contact  with  the  ball  b,  which  was  dragging  past 
its  front.  Amoeba  c  thereupon  turned,  followed  Amoeba  a,  and  began 
to  engulf  the  ball  b.  A  cavity  was  formed  in  the  anterior  part  of  Amoeba 
c,  reaching  back  nearly  or  quite  to  its  middle,  and  much  more  than 
sufficient  to  contain  the  ball  b.  Amoeba  a  now  turned  into  a  new  path ; 
Amoeba  c  followed  (Fig.  21,  at  4).  After  the  pursuit  had  lasted  for 
some  time  the  ball  b  had  become  completely  enveloped  by  Amoeba  c. 
The  cord  connecting  the  ball  with  Amoeba  a  broke,  and  the  latter  went 
on  its  way,  disappearing  from  our  account.  Now  the  anterior  opening 
of  the  cavity  in  Amoeba  c  became  partly  closed,  leaving  only  a  slender 
canal  (5).  The  ball  b  was  thus  completely  enclosed,  together  with  a  quan- 
tity of  water.  There  was  no  adhesion  between  the  protoplasm  of  b  and 
c;  on  the  contrary,  as  the  sequel  will  show  clearly,  both  remained  inde- 
pendent, c  merely  enclosing  b. 

Now  the  large  Amoeba  c  stopped,  then  began  to  move  in  another 
direction  (Fig.  21,  at  5-6),  carrying  with  it  its  meal.  But  the  meal  — 
the  ball  b  —  now  began  to  show  signs  of  life,  sent  out  pseudopodia,  and  be- 
came very  active ;  we  shall  therefore  speak  of  it  henceforth  as  Amoeba  b. 
It  began  to  creep  out  through  the  still  open  canal,  sending  forth  its 
pseudopodia  to  the  outside  (7).  Thereupon  Amoeba  c  sent  forth  its 
pseudopodia  in  the  same  direction,  and  after  creeping  in  that  direction 
several  times  its  own  length,  again  enclosed  b  (7,  8).  The  latter  again 
partly  escaped  (9),  and  was  again  engulfed  completely  (10).  Amoeba  c 
now  started  again  in  the  opposite  direction  (11),  whereupon  Amoeba  b, 
by  a  few  rapid  movements,  escaped  from  the  posterior  end  of  Amoeba 
c,  and  was  free,  — being  completely  separated  from  c  (11,  12).  There- 
upon c  reversed  its  course  (12),  overtook  b,  engulfed  it  completely  again 
(13),  and  started  away.  Amoeba  b  now  contracted  into  a  ball  and  re- 
mained quiet  for  a  time.  Apparently  the  drama  was  over.  Amoeba  c 
went  on  its  way  for  about  five  minutes  without  any  sign  of  life  in  b.  In 
the  movements  of  c  the  ball  became  gradually  transferred  to  its  poste- 
rior end,  until  there  was  only  a  thin  layer  of  protoplasm  between  b  and 
the  outer  water.  Now  b  began  to  move  again,  sent  pseudopodia  through 
the  thin  wall  to  the  outside,  and  then  passed  bodily  out  into  the  water 
(14).     This  time  Amoeba  c  did  not  return  and  recapture  b.     The  two 


18  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

Amoebae  moved  in  opposite  directions  and  became  completely  separated. 
The  whole  performance  occupied  about  fifteen  minutes. 

Such  behavior  is  evidently  complex.  An  analysis  into  simple  re- 
actions to  simple  stimuli  is  difficult  if  possible  at  all.  We  shall  return 
to  this  matter  later. 

The  method  of  food-taking  illustrated  in  the  behavior  described  is 
characteristic  for  Amoebae  of  the  proteus  and  Umax  types.  It  is  some- 
times said  that  these  Amoebae  take  food  at  the  wrinkled  posterior  end. 
This,  if  true  at  all,  is  certainly  rare;  the  author  has  never  observed  it, 
though  he  has  seen  food  taken  in  dozens  of  cases.  The  essential  fea- 
tures of  the  food  reaction  seem  to  be  the  movement  of  the  Amoeba 
toward  the  food  body  (long  continued,  in  some  cases),  the  hollowing  out 
of  the  anterior  end  of  the  Amoeba,  the  sending  forth  of  pseudopodia 
on  each  side  of  and  above  the  food,  and  the  fusion  of  the  free 
ends  of  the  pseudopodia,  thus  enclosing  the  food,  with  a  quantity 
of  water.  The  reaction  is  thus  complex;  at  times,  as  we  have  seen, 
extremely  so. 

In  the  process  of  taking  food  which  we  have  just  described  there  is 
no  adherence  between  the  protoplasm  and  the  food  body.  But  in 
A  mceba  verrucosa  and  its  relatives  foreign  objects  do  adhere  to  the  sur- 
face of  the  body,  and  this  adherence  is  of  much  assistance  in  obtaining 
food.  It  partly  compensates  for  the  lack  of  pseudopodia  in  these  species. 
But  it  is  not  alone  food  substances  that  cling  to  the  surface  of  the  body. 
Particles  of  soot  and  bits  of  debris  of  all  sorts  become  attached  in  the 
same  way.  Not  all  these  substances  are  taken  into  the  body  as  food, 
so  that  adhesion  to  the  surface  does  not  account  for  food-taking.  For 
this  an  additional  reaction  is  necessary. 

Food-taking  in  Amoeba  verrucosa  often  occurs  as  follows:  The  ani- 
mal in  its  progress  comes  in  contact  with  a  small  food  body,  such  as  a 
Euglena  cyst.  This  adheres  to  the  surface,  and  may  pass  forward  on 
the  upper  surface  of  the  body  to  the  anterior  edge,  in  the  way  described 
on  a  previous  page.  At  the  same  time  it  begins  to  sink  slowly  into  the 
body,  surrounded  by  a  layer  of  ectosarc.  When  it  has  rounded  the 
anterior  edge,  the  Amoeba  passes  over  it ;  then  the  food  body  passes  up- 
ward again  at  the  posterior  end  and  forward  on  the  upper  surface.  It 
is  now  sunk  still  more  deeply  into  the  protoplasm,  and  by  the  time  it 
reaches  the  anterior  edge  again  it  has  usually  passed  completely  into  the 
endosarc,  together  with  the  layer  of  ectosarc  enveloping  it.  In  this  way 
the  author  has  seen  Amoeba  verrucosa  ingest  various  algas,  small  flagel- 
lates, Euglena  cysts,  and  a  small  Amoeba  of  the  proteus  type.  Indifferent 
particles,  such  as  bits  of  soot,  which  are  attached  to  the  surface  at  the 
same  time,  are  not  taken  in. 


THE  BEHAVIOR   OF   AMCEBA 


19 


Sometimes  the  taking  of  food  is  in  Amoeba  verrucosa  a  much  more 
complicated  process  than  that  just  described.  Rhumbler  (1898)  has 
given  a  very  interesting  account  of  the  way  in  which  this  species  feeds 
upon  filaments  of  algae 
many  times  its  own 
length  (Fig.  22).  The 
animal  settles  upon 
the  middle  of  an 
Oscillaria  filament,  en- 
velopes it,  and  length- 
ens out  along  it  (a). 
Then  one  end  bends 
over  (b),  so  that  a  loop 
is  formed  in  the  fila- 
ment (c).  The  Amceba 
then  stretches  out  on 
the  filament  again, 
bends  it  over  anew, 
and  the  process  is 
repeated  until  the  fila- 
ment forms  a  close  coil  within  the  Amceba  (c  to  g,  Fig.  22).  Leidy 
(1879,  P-  86)  has  given  a  similar  account  of  the  method  of  feeding  on 
filaments  of  algae  in  Dinamceba. 

Filaments  that  have  been  partly  coiled  up  are  often  ejected  when 
light  is  thrown  upon  the  animal  (Rhumbler,  1898). 


Fig.  22.  —  Amceba  verrucosa  coiling  up  and  ingesting  a  fila- 
ment of  Oscillaria.  After  Rhumbler  (1898).  The  letters  a  to  g 
show  successive  stages  in  the  process. 


Features  of  General  Significance  in  the  Behavior 

of  Amceba 


We  find  that  the  simple  naked  mass  of  protoplasm  reacts  to  all 
classes  of  stimuli  to  which  higher  animals  react  (if  we  consider  auditory 
stimulation  merely  a  special  case  of  mechanical  stimulation).  Mechan- 
ical stimuli,  chemical  stimuli,  temperature  differences,  light,  and  elec- 
tricity control  the  direction  of  movement,  as  they  do  in  higher  animals. 
In  other  words,  Amceba  has  some  method  of  responding  to  all  the  chief 
classes  of  life  conditions  which  it  meets. 

The  cause  of  a  reaction  —  that  is,  of  a  change  of  movement  —  is  in 
most  cases  some  change  in  the  environment,  due  either  to  an  actual 
alteration  of  the  conditions,  or  to  the  movement  of  the  animal  into  new 
conditions.  This  is  notably  true  of  the  reactions  to  mechanical,  chemi- 
cal, and  thermal  stimuli.     In  the  reactions  to  light  and  the  electric  cur- 


20  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

rent  this  is  not  so  evident  at  first  view.  The  Amoeba  reacts  even  though 
the  light  or  current  remains  constant.  But  if,  as  appears  to  be  true,  the 
stimulation  occurs  primarily  on  that  side  on  which  the  light  shines,  or  on 
the  anode  side  in  the  reaction  to  electricity,  then  it  is  true  that  even  in 
these  cases  the  reacting  protoplasm  is  subjected  to  changes  of  conditions. 
Since  the  movement  of  the  Amoeba  is  of  a  rolling  character,  the  proto- 
plasm of  the  anterior  end  and  that  of  the  posterior  end  continually  in- 
terchange positions.  In  an  Amoeba  moving  toward  the  cathode  the 
extended  protoplasm  at  the  cathode  end  is  gradually  transferred  to  the 
anode  end,  and  as  this  change  takes  place  it  contracts.  In  the  reaction 
to  light  the  protoplasm  of  the  anterior  end  directed  away  from  the  light 
is  gradually  transferred  in  the  rolling  movement  to  the  lighted  side;  it 
then  contracts.  It  is  therefore  possible  that  in  these  cases  also  it  is  the 
change  from  one  condition  to  another  that  causes  reaction. 

It  is  notable  that  changes  from  one  condition  to  another  often  cause 
reaction  when  neither  the  first  condition  nor  the  second  would,  if  acting 
continuously,  produce  any  such  effect.  Thus,  Amoebae  react  negatively 
to  tap  water  or  to  water  from  a  foreign  culture,  but  after  transference  to 
such  water  they  behave  normally.  Harrington  and  Learning  (1900) 
show  that  when  white  light  is  thrown  on  an  Amoeba  it  ceases  to  move, 
but  if  this  light  continues,  the  animal  resumes  movement.  To  constant 
conditions  Amoeba  tends  to  become  acclimatized. 

But  even  constant  conditions  may  induce  reaction  if  they  interfere 
seriously  with  the  life  activities  of  the  animal.  Under  great  heat  or 
strong  chemicals  the  protoplasm  contracts  irregularly  and  remains  thus 
contracted  till  death  follows.  A  different  example  of  the  production  of 
a  reaction  by  constant  conditions  is  shown  in  the  behavior  of  Amoebae 
suspended  in  the  water.  Under  these  conditions,  as  we  have  seen,  the 
animal  sends  pseudopodia  in  all  directions,  taking  a  starlike  form.  It 
is  evident  that  the  general  condition  of  the  organism,  as  well  as  an 
external  change,  may  determine  a  reaction. 

The  fact  that  the  nature  of  the  behavior  depends  on  the  general  con- 
dition of  the  organism  is  illustrated  in  another  way  by  the  observation 
of  Rhumbler,  that  Amoebae  may  begin  to  take  food,  then  suddenly  reject 
it.  This  rejection  occurs  especially  after  subjection  to  light.  Appar- 
ently the  light  changes  the  condition  of  the  animal  in  such  a  way  that  it 
no  longer  reacts  to  food  as  it  did. 

In  Amoeba,  as  in  higher  animals,  the  localization  of  the  stimulation 
partially  determines  the  reaction.  The  result  of  stimulation  on  the 
right  side  is  to  cause  movement  in  a  direction  different  from  that  pro- 
duced by  stimulation  on  the  left  side.  In  Amoeba  the  relation  of  the 
movement  to  the  localization  of  the  stimulus  is  very  simply  determined, 


THE  BEHAVIOR   OF   AMCEBA  21 

through  the  fact  that  it  is  primarily  the  part  stimulated  that  responds. 
This  part  contracts  or  extends,  thus  partly  determining  the  direction  of 
movement. 

But  the  localization  of  the  external  stimulus  is  not  the  only  factor  in 
determining  the  direction  of  locomotion.  Especially  in  the  negative 
reactions  certain  other  factors  are  evident,  which  are  of  much  impor- 
tance for  understanding  the  behavior.  After  stimulation  at  one  side  or 
end,  the  new  pseudopodium  is  as  a  rule  not  sent  out  in  a  direction 
exactly  opposite  that  from  which  the  stimulation  comes.  It  usually  ap- 
pears, as  we  have  seen,  on  some  part  of  the  original  anterior  end  of  the 
body,  and  at  first  alters  the  course  only  slightly.  This  is  evidently  con- 
nected with  the  fact  that  only  the  anterior  end  is  attached  to  the  sub- 
stratum, and  without  such  attachment  locomotion  cannot  occur.  If  the 
pseudopodium  were  sent  out  from  the  unattached  posterior  part  of  the 
body,  it  would  have  to  overcome  the  resistance  of  the  contraction  existing 
there,  and  would  have  to  find  the  substratum  and  become  attached  to  it. 
The  new  pseudopodium  thus  starts  out  from  the  region  of  least  resist- 
ance, and  in  such  a  way  that  the  new  movement  forms  a  continuation 
of  the  original  one,  though  in  a  different  direction.  If  the  new  direction 
still  leaves  the  anterior  part  of  the  body  exposed  to  the  action  of  the 
stimulus,  then  a  new  pseudopodium  is  sent  out  in  the  same  way,  still 
further  altering  the  course.  This  may  continue  till  the  original  direc- 
tion of  locomotion  is  squarely  reversed. 

This  is  the  method  of  changing  the  course  that  is  usually  seen  in 
the  reactions  to  mechanical  (Fig.  9),  chemical  (Fig.  15),  thermal,  and 
electric  (Fig.  17)  stimuli.  From  Davenport's  figures  (Fig.  16)  it  ap- 
pears to  be  likewise  the  method  in  the  reactions  to  light. 

From  these  facts  it  is  clear  that  the  direction  of  movement  in  a  nega- 
tive reaction  is  not  determined  entirely  by  the  position  of  the  stimulat- 
ing agent  or  the  part  of  the  body  on  which  it  acts.  The  moving  Amoeba 
is  temporarily  differentiated,  having  two  ends  of  opposite  character, 
while  the  two  sides  differ  from  the  ends.  These  internal  factors  play 
a  large  part  in  determining  the  direction  of  movement ;  the  present  action 
of  Amoeba,  even  when  responding  to  stimuli,  depends,  as  a  result  of  these 
temporary  differentiations,  partly  on  its  past  action.  The  new  pseu- 
dopodium will  be  sent  out  under  most  circumstances  from  some  part 
of  the  anterior  end,  only  under  special  conditions  from  a  side,  and  still 
more  rarely  from  the  posterior  end.  We  have  here  the  first  traces  of 
relations  which  play  large  parts  in  the  behavior  of  animals  higher  than 
Amoeba.  Structural  differentiations  have  become  permanent  in  most 
animals,  and  as  such  play  a  most  important  role  in  determining  the 
direction  of  movement.     Further,  in  practically  all  animals  the  past 


22  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

actions  are,  as  in  Amoeba,  important  factors  in  determining  reactions 
to  present  stimuli.  In  Amoeba  we  see  in  the  simplest  way  the  effects  of 
past  stimuli  and  past  reactions  in  determining  present  behavior. 

As  a  result  of  this  interplay  of  external  and  internal  factors  in  deter- 
mining movement,  the  avoidance  of  a  stimulating  agent  usually  occurs 
in  Amceba  by  a  process  which  we  should  call  in  higher  animals  one  of 
trial.  If  the  movement  were  directly  and  unequivocally  determined  by 
the  localization  of  the  stimulus,  there  would  be  nothing  involved  that 
could  be  compared  to  a  trial.  The  direct  withdrawal  of  the  part  stimu- 
lated is  a  factor  due  immediately  to  the  localization  of  the  external  agent. 
But  the  sending  forth  of  a  pseudopodium  in  a  new  direction  is  not  forced 
by  the  external  agent,  but  is  an  outflow  of  the  internal  energy  of  the 
organism,  and  the  position  of  this  new  pseudopodium  is,  as  we  have 
seen,  determined  by  internal  conditions.  The  latter  factors  are  those 
which  correspond  to  the  activities  that  we  call  trial  in  higher  animals. 
If  the  new  direction  of  movement  leads  to  further  stimulation,  a  new 
trial  is  made.  Such  trials  are  repeated  till  either  there  is  no  further 
stimulation,  or  if  it  is  not  possible  to  escape  completely,  until  the  stimu- 
lation falls  on  the  posterior  end,  and  the  animal  is  retreating  directly 
from  the  source  of  stimulation. 

The  entire  reaction  method  may  be  summed  up  as  follows:  The 
stimulus  induces  movement  in  various  directions  (as  defined  by  internal 
causes).  One  of  these  directions  is  then  selected  through  the  fact  that 
by  subjecting  the  animal  to  new  conditions,  it  relieves  it  from  stimula- 
tion. This  is  our  first  example  of  "selection  from  among  the  conditions 
produced  by  varied  movements,"  —  a  phenomenon  playing  a  large  part, 
as  we  shall  see,  in  the  behavior  of  organisms. 

The  method  of  reaction  above  described  gives,  with  different  stimuli, 
two  somewhat  differing  classes  of  results.  In  the  reactions  to  mechani- 
cal, chemical,  and  thermal  stimuli,  different  directions  are  "tried"  until 
the  organism  is  moving  in  such  a  direction  that  it  is  no  longer  subjected 
to  the  stimulating  agent ;  in  this  direction  it  continues  to  move.  But  in 
the  reactions  to  light  and  to  electricity  new  directions  are  tried  merely 
until  the  stimulation  falls  upon  the  posterior  end,  and  the  organism  is 
retreating  directly  from  the  source  of  stimulation.  There  is  no  possibil- 
ity of  escaping  the  stimulating  agent  completely.  In  the  reactions  to  the 
two  stimuli  last  mentioned  the  long  axis  of  the  animal  must  after  a  time 
take  up  a  definite  orientation  with  respect  to  the  direction  from  which 
the  stimulus  comes,  while  in  the  reactions  to  other  stimuli  there  is  usually 
no  such  orientation.  This  difference  is  due,  not  to  any  essentially  dif- 
ferent method  of  reacting  in  the  two  cases,  but  merely  to  the  peculiar 
distribution  of  the  stimulating  agents ;   light  and  electricity  act  continu- 


THE  BEHAVIOR   OF  AMCEBA  23 

ously,  and  always  affect  a  certain  side  of  the  organism,  while  this  is  not 
true  of  the  other  agents. 

If  an  intense  stimulus  acts  on  the  entire  surface  of  Amoeba  at  once, 
the  animal  contracts  irregularly  and  ceases  to  move.  If  the  acting  agent 
is  very  powerful,  the  Amoeba  may  remain  contracted  till  it  dies ;  other- 
wise it  usually  soon  begins  locomotion  again. 

We  may  classify  the  various  changes  in  behavior  due  to  stimulation 
into  three  main  types,  which  may  be  called  the  positive  reaction,  the 
negative  reaction,  and  the  food  reaction;  these  have  already  been  de- 
scribed in  detail.  These  types  are  not  stereotyped;  each  varies  much 
in  details  under  different  conditions.  The  movements  in  these  reactions 
are  clearly  not  the  direct  results  of  the  simple  physical  action  of  the 
agents  inducing  them  (see  Jennings,  1904  g).  As  in  higher  animals,  so 
in  Amoeba,  the  reactions  are  indirect.  The  effect  of  external  agents  is 
to  cause  internal  alterations,  and  these  determine  the  movements.  It 
is  therefore  not  possible  to  predict  the  movements  of  the  organism  from 
a  knowledge  of  the  direct  physical  changes  produced  in  its  substance  by 
the  agent  in  question. 

What  decides  whether  the  reaction  to  a  given  stimulus  shall  be  posi- 
tive or  negative?  This  question  touches  the  fundamental  problem  of 
behavior.  The  nature  of  the  physical  or  chemical  action  of  an  agent 
does  not  alone  determine  the  reaction,  for  to  the  same  agent  opposite 
reactions  may  be  given,  depending  on  its  intensity,  or  upon  various 
attendant  circumstances.  If  we  should  make  a  chemical  or  physical 
classification  of  the  agents  affecting  movement  in  Amoeba,  this  would 
not  coincide  with  a  classification  based  on  the  reactions  given.  But  the 
agents  which  produce  a  negative  reaction  are  in  general  those  which 
injure  the  organism  in  one  way  or  another,  while  those  inducing  the 
positive  reaction  are  beneficial.  Any  agent  which  directly  injures  the 
animal,  such  as  strong  chemicals,  heat,  mechanical  impact,  produces 
the  negative  reaction.  The  positive  reaction  is  known  to  be  produced 
only  by  agents  which  are  beneficial  to  the  organism.  It  aids  the  animal 
to  find  solid  objects  on  which  it  can  move,  and  is  the  chief  factor  in 
obtaining  food.  Thus  the  behavior  of  Amoeba  is  directly  adaptive ;  it 
tends  to  preserve  the  life  of  the  animal  and  to  aid  it  in  carrying  on  its 
normal  activities. 

It  may  perhaps  be  maintained  that  certain  reactions  are  not  adap- 
tive ;  for  example,  that  to  the  electric  current.  The  reaction  in  this  case 
does  not  tend  to  remove  the  organism  from  the  action  of  the  stimulat- 
ing agent.  But  it  is  instructive  to  imagine  in  such  a  case  an  organism 
with  possibilities  of  high  intelligence  —  say  even  a  human  being  — 
placed  under  similar  conditions,  with  similar  limitations  of  sense  and 


24  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

of  locomotive  power.  Would  it  give  a  more  adaptive  reaction  than 
Amoeba?  Evidently,  the  conditions  are  such  that  it  is  impossible  for 
the  animal  to  escape  by  any  means  from  the  current.  Since  the  stimu- 
lation apparently  comes  most  strongly  from  the  anode  side,  it  is  natural 
to  move  in  the  opposite  direction.  The  method  of  the  negative  reaction 
is  that  of  a  trial  of  certain  directions  of  movement.  This  method  is  in 
essence  an  adaptive  one,  and  if  it  fails  in  the  present  case,  certainly  no 
better  course  of  action  can  be  suggested. 

Can  the  behavior  of  Amoeba  be  resolved  throughout  into  direct 
unvarying  reactions  to  simple  stimuli,  —  into  elements  comparable  to 
simple  reflexes  ? 

For  most  of  the  behavior  described  in  the  preceding  pages  the  stimuli 
can  be  recognized  in  simple  chemical  or  physical  changes  in  the  environ- 
ment. Yet  there  are  certain  trains  of  action  for  which  such  a  resolution 
into  unvarying  reactions  to  simple  stimuli  seems  unsatisfactory.  This 
is  notably  true  for  some  of  the  food  reactions.  In  watching  an  Amoeba 
following  a  rolling  food  ball,  as  in  Fig.  19,  one  seems  to  see  the  animal, 
after  failing  to  secure  the  food  in  one  way,  try  another.  Again,  in  the 
pursuit  of  one  Amoeba  by  another,  it  is  difficult  to  conceive  each  phase 
of  action  of  the  pursuer  to  be  completely  determined  by  a  simple  present 
stimulus.  For  example,  in  Fig.  21,  after  Amoeba  b  has  escaped  com- 
pletely and  is  quite  separate  from  Amoeba  c,  the  latter  reverses  its 
course  and  recaptures  b  (at  n-13).  What  determines  the  behavior  of 
c  at  this  point  ?  If  we  can  imagine  all  the  external  physical  and  chemi- 
cal conditions  to  remain  the  same,  with  the  two  Amoebae  in  the  same 
relative  positions,  but  suppose  at  the  same  time  that  Amoeba  c  has  never 
had  the  experience  of  possessing  b,  —  would  its  action  be  the  same  ? 
Would  it  reverse  its  movement,  take  in  b,  then  return  on  its  former 
course?  One  who  sees  the  behavior  as  it  occurs  can  hardly  resist  the 
conviction  that  the  action  at  this  point  is  partly  determined  by  the 
changes  in  c  due  to  the  former  possession  of  b,  so  that  the  behavior  is 
not  purely  reflex. 

Of  less  interest  than  the  case  just  mentioned  are  modifications  in 
behavior  due  to  acclimatization,  and  to  the  interference  of  stimuli. 
Amoeba  may  become  accustomed  to  certain  things,  so  as  to  cease  reacting 
after  a  time,  though  the  condition  remains  the  same.  Thus  Verworn 
(1889  b)  found  that  Amoebae  which  at  first  react  to  a  weak  electric  cur- 
rent may  after  a  time  continue  their  usual  movements,  without  regard 
to  the  current.  Harrington  and  Learning  (1900),  as  we  have  seen,  found 
that  white  or  blue  light  thrown  on  Amoeba  causes  it  to  cease  moving,  but 
if  the  light  is  continued,  the  movements  begin  again  after  a  time.  In- 
deed, we  have  recognized  above  the  general  fact  that  change  is  the  chief 


THE  BEHAVIOR   OF  AMCEBA  25 

factor  in  causing  reaction,  so  that  such  acclimatization  is  a  constant, 
normal  factor  in  the  behavior.  A  change  in  reaction  due  to  a  different 
cause  is  seen  in  Rhumbler's  observation  of  the  fact  that  Amoeba  after 
beginning  to  ingest  food  may  reject  it  when  subjected  to  light. 

Beyond  facts  of  this  character,  little  is  known  as  to  the  modifiability 
of  reactions  in  Amoeba. 

LITERATURE  I 

(Works  are  cited  here  by  giving  the  author's  name  followed  by  the  date  of  publi- 
cation. The  full  title  will  be  found  in  the  alphabetical  list  at  the  end  of  the  volume. 
Only  the  important  works  are  mentioned.) 

A.  General  account  of  the  behavior  of  Amoeba,  giving  details  of  the  observations 
on  which  the  foregoing  account  is  mainly  based  :  Jennings,  1904  e. 

B.  Attempted  physical  explanations  of  the  activities  of  Amoeba :  Rhumbler, 
1898;  .Butschli,  1892;  Bernstein,  1900;  Jensen,  1901,  1902;  Verworn,  1892; 
Jennings,  1902  a,  1904  £-;  Rhumbler,  1905. 

C.  General  works  on  Amoeba  and  its  relatives  :  Butschli,  1880 ;  Penard,  1902  ; 
Leidy,  1879. 

D.  Reactions  to  unlocalized  stimuli,  and  to  localized  heat:  Verworn,  1889. 

E.  Reaction  to  electricity:  Verworn,  1889  b,  1896  a;  Jennings,  1904  £. 

F.  Reactions  to  light:  Davenport,  1897;  Harrington  and  Leaming,  1900; 
Engelmann,  1879. 


CHAPTER   II 


THE   BEHAVIOR   OF   BACTERIA 


i.   Structure  and  Movements 


Bacteria  are  perhaps  the  lowest  organisms  having  a  definite  form 
and  special  organs  for  locomotion.  In  these  characteristics  they  are  less 
simple  than  Amoeba  and  resemble  higher  animals,  though  in  other  ways 
the  bacteria  are  among  the  simplest  of  organisms.  Whether  they  are 
more  nearly  related  to  animals  or  to  plants  is  a  question  of  little  impor- 
tance for  our  purposes ;  they  are  usually  considered  as  nearer  to  plants. 
Bacteria  are  minute  organisms  living  in  immense  numbers  in  decay- 
ing organic  matter,  and  found  in  smaller  numbers  almost  everywhere. 

They  have  characteristic  definite 
forms  (Fig.  23) ;  some  are  straight 
cylindrical  rods;  some  are  curved 
rods;  some  are  spiral  in  form; 
others  are  spherical,  oval,  or  of 
other  shapes.  The  individuals  are 
often  united  together  in  chains. 

While   some  bacteria  are  quiet, 

others   move   about  rapidly.     The 

movements    are    produced    by   the 

swinging  of  whiplike  protoplasmic 

-  Difterent  species  of  bacteria,    processes,  the  flagella  or  cilia.     The 

flagella  may  be  borne  singly  or  in 
numbers  at  one  end  of  the  body, 
or  may  be  scattered  over  the  entire 
surface.  Figure  23  shows  the  dis- 
tribution of  flagella  in  a  number 
of  species. 
In  most  bacteria  we  can  distinguish  a  permanent  longitudinal  axis, 
and  along  this  axis  movement  takes  place.  Thus  both  the  form,  and  in 
correspondence  with  it,  the  movement,  are  more  definite  than  in  Amceba. 
If  the  bacterium  is  quiet,  we  can  predict  that  when  it  moves  it  will  move 
in  the  direction  of  this  axis;    for  Amceba  such  a  prediction  cannot  be 

26 


Fig. 

showing  the  distribution  of  the  flagella.  a. 
Chromatium  •  okeni,  after  Zopf ;  b,  Chro- 
matium  photomctriciim,  after  Engelmann  ; 
c,  Spirillum  undula,  after  Migula;  d,  Vibrio 
cholera,  after  Fischer  ;  e,  Bacilli  of  typhus, 
after  Fischer  ;  /,  Bacillus  syncyaneus,  after 
Fischer  ;  g,  Clostridium  butyricum,  after 
Fischer. 


THE  BEHAVIOR   OF  BACTERIA  27 

made.  In  some  bacteria  the  two  ends  are  similar,  and  movement  may 
take  place  in  either  direction.  In  others  the  two  ends  differ,  one  bearing 
flagella,  while  the  other  does  not.  In  these  species  the  movement  is  still 
further  determined ;  the  end  bearing  the  flagella  is  anterior  in  the  usual 
locomotion.  In  none  of  the  bacteria  can  we  distinguish  upper  and  lower 
surfaces  or  right  and  left  sides.  As  the  bacterium  swims,  it  revolves 
continually  on  its  long  axis;  the  significance  of  this  revolution  will  be 
considered  in  our  account  of  behavior  in  the  infusoria. 


2.  Reactions  to  Stimuli 

The  movements  of  the  bacteria  are  not  unordered,  but  are  of  such  a 
character  as  to  bring  about  certain  general  results,  some  of  which  at 
least  are  conducive  to  the  welfare  of  the  organism.  If  a  bacterium 
swimming  in  a  certain  direction  comes  against  a  solid  object,  it  does 
not  remain  obstinately  pressing  its  anterior  end  against  the  object,  but 
moves  in  some  other  direction.  If  some  strong  chemical  is  diffusing  in 
a  certain  region,  the  bacteria  keep  out  of  this  region  (Fig.  24).  They 
often  collect  about  bubbles  of  air,  and  about  masses  of  decaying  animal 
or  plant  material.  Often  they  gather  about  small  green  plants  (Fig.  25), 
and  in  some  cases  a  large  number  of  bacteria  gather  to  form  a  well- 
defined  group  without  evident  external  cause. 

How  are  such  results  brought  about  ?  To  answer  this  question,  we 
will  examine  carefully  the  behavior  of  the  large  and  favorable  form, 
Spirillum1  (Fig.  23,  c).  Spirillum  is  a  spiral  rod,  bearing  a  bunch  of 
flagella  at  one  end.  In  a  thriving  culture  a  large  proportion  of  the  indi- 
viduals bear  flagella  at  both  ends  and  can  swim  indifferently  in  either 
direction.  It  is  said  by  good  authorities  that  such  specimens  are  pre- 
paring to  divide. 

When  Spirillum  comes  against  an  obstacle,  it  responds  by  the  sim- 
plest possible  reaction,  —  by  a  reversal  of  the  direction  of  movement. 
In  specimens  with  flagella  at  each  end  the  new  direction  is  continued 
till  a  new  stimulation  causes  a  new  reversal.  In  bacteria  with  flagella 
at  only  one  end,  the  movement  backward  is  continued  only  a  short  time, 
then  the  forward  movement  is  resumed.  Usually  when  the  forward 
movement  is  renewed,  the  path  followed  is  not  the  same  as  the  original 
path,  but  forms  an  angle  with  it ;  the  bacterium  has  thus  turned  to  one 
side.     Whether  this  turning  is  due  to  currents  in  the  water  or  other 

1  There  are  several  species  of  Spirillum  found  in  decaying  organic  matter.  The  species 
have  not  been  clearly  determined  in  most  of  the  work  on  behavior,  and  this  is  not  of  great 
importance,  as  the  behavior  is  essentially  the  same  in  character  throughout. 


28 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


accidental  conditions,  or,  as  is  more  probable,  is  determined  in  some  way 
by  the  structure  of  the  organisms,  has  not  been  discovered.  In  the 
infusoria,  as  we  shall  see,  the  latter  is  the  case. 

The  reversal  of  movement  of  course  carries  the  organism  away  from 
the  agent  causing  it.  We  find  that  the  same  reaction  is  produced  when 
the  bacterium  comes  to  a  region  where  some  repellent  chemical  is  diffus- 
ing in  the  water.  This  is  well  shown  when  a  drop  of  jr  per  cent  NaCl  is 
introduced  with  a  capillary  pipette  beneath  the  cover-glass  of  a  prepara- 
tion swarming  with  actively  moving  Spirilla.  The  bacteria  at  first  keep 
up  their  movement  in  all  directions,  but  on  coming  to  the  edge  of  the 
drop  of  salt  solution  the  movement  is  reversed.  Hence  none  of  the  bacteria 
enter  the  drop,  and  it  remains  empty,  like  the  chemicals  in  Fig.  24. 


B 


Fig.  24.  —  Repulsion  of  bacteria  by  chemicals.  A.  Repulsion  of  Chromatium  ivcissii  by 
malic  acid  diffusing  from  a  capillary  tube.  After  Miyoshi  (1897).  B,  Repulsion  of  Spirilla  by 
crystals  of  NaCl.  a,  Condition  immediately  after  adding  the  crystals;  b  and  c,  later  stages 
in  the  reaction.     After  Massart  (1891). 


They  react  in  this  way  toward  solutions  of  most  acids  and  alkalies,  as 
well  as  toward  many  salts  and  other  chemicals.  A  drop  of  these  chem- 
icals remains  entirely  empty  when  introduced  into  a  preparation  of 
Spirilla. 

This  simple  reversal  of  movement  is  the  method  by  which  avoidance 
of  any  agent  takes  place ;  in  other  words,  it  is  the  method  of  the  nega- 
tive reactions  in  bacteria.  Bacteria  also  collect  in  certain  regions,  as  we 
have  seen,  —  about  air  bubbles,  green  plants,  food,  etc. ;  they  have 
thus  what  are  called  "positive  reactions"  as  well  as  negative  ones. 
What  is  the  behavior  in  the  formation  of  such  collections? 

One  finds,  rather  unexpectedly,  that  the  positive  reaction  is  produced 
in  essentially  the  same  way  as  the  negative  one,  —  by  a  simple  reversal 


THE  BEHAVIOR   OF  BACTERIA  29 

of  movement  under  certain  conditions.  If  we  place  water  containing 
many  Spirilla  on  a  slide,  allowing  some  small  air  bubbles  to  remain  be- 
neath the  cover-glass,  we  find  after  a  time  that  the  bacteria  are  collecting 
about  the  bubbles.  The  course  of  events  in  forming  the  collections  is 
seen  to  be  as  follows:  At  first  the  Spirilla  are  scattered  uniformly, 
swimming  in  all  directions.  They  pass  close  to  the  air  bubble  without 
change  in  the  movements.  But  gradually  the  oxygen  throughout  the 
preparation  becomes  used  up,  while  from  the  air  bubble  oxygen  diffuses 
into  the  water.  After  a  time  therefore  the  bubble  must  be  conceived  as 
surrounded  by  a  zone  of  water  impregnated  with  oxygen.  Now  the  bac- 
teria begin  to  collect  about  the  bubble.  They  do  not  change  their  direc- 
tion of  movement  and  swim  straight  toward  the  center  of  diffusion  of 
the  oxygen.  On  the  contrary  the  movement  continues  in  all  directions 
as  before.  A  Spirillum  swimming  close  to  the  bubble  into  the  oxygen- 
ated zone  does  not  at  first  change  its  movement  in  the  least.  It  swims 
across  the  zone  until  it  reaches  the  other  side,  where  it  would  again 
pass  out  into  the  water  containing  no  oxygen.  Here  the  reaction  oc- 
curs ;  the  organism  reverses  its  movement  and  swims  in  the  opposite 
direction.  If  the  specimen  has  flagella  at  each  end,  it  continues  its  re- 
versed movement  until  the  opposite  side  of  the  area  containing  the  oxygen 
is  reached ;  then  the  movement  is  reversed  again.  This  is  continued, 
the  direction  of  movement  being  reversed  as  often  as  the  organism 
comes  to  the  outer  boundary  of  the  zone  of  oxygen  within  which  it  is  swim- 
ming.1 Thus  the  bacterium  oscillates  back  and  forth  across  the  area  of 
oxygen.  Specimens  having  flagella  at  but  one  end  swim  backward 
only  a  short  distance  after  reaching  the  boundary  of  the  area,  then  start 
forward  again. 

As  a  result  of  this  way  of  acting  the  bacterium  of  course  remains  in 
the  oxygenated  area.  The  latter  thus  retains  every  bacterium  that 
enters  it.  Many  bacteria,  swimming  at  random,  enter  the  area  in  the 
way  described,  react  at  the  outer  boundary,  and  remain ;  thus  in  the 
course  of  time  the  area  of  oxygen  swarms  with  the  organisms,  while 
the  surrounding  regions  are  almost  free  from  them.  The  finding  of  the 
oxygen  then  depends  upon  the  usual  movements  of  the  bacteria,  —  not 
upon  movements  specially  set  in  operation  or  directed  by  the  oxygen. 

Thus  the  positive  and  negative  reactions  of  the  bacteria  are  pro- 
duced in  the  same  way;  both  take  place  through  the  reversal  of  the 
movement  when  stimulated.  The  stimulus  is  some  change  in  the  na- 
ture of  the  surrounding  medium.  In  the  negative  reaction  the  change 
is  from  ordinary  water  to  water  containing  some  chemical;   in  the  posi- 

1  The  bacterium  may  of  course  come  against  the  bubble  itself ;  the  movement  is  then 
reversed  in  the  same  way. 


30  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

tive  reaction  it  is  the  change  from  water  containing  oxygen  to  water  con- 
taining none. 


■r-:iz$£'&-. 


'  :',;'*%s!'gi.-:  : 


A  B 

Fig.  25.  —  Collections  of  bacteria  about  algae,  due  to  the  oxygen  produced  by  the  latter. 
A,  Spirilla  collected  about  a  diatom.  After  Verworn.  B,  Bacteria  gathered  about  a  spherical 
green  alga  cell  in  the  light,  a  shows  the  condition  immediately  after  placing  the  bacteria  and 
alga  on  a  slide;  no  collection  has  yet  formed,  b,  Condition  two  minutes  later;  part  of  the  bac- 
teria have  gathered  closely  about  the  cell.     After  Engelmann  (1894). 


\  .'. 


■■;<; 


Spirilla  collect  in  the  way  above  described  about  any  source  of  oxy- 
gen. Green  plants  give  off  oxygen  in  the  light,  so  that  the  bacteria  col- 
.._  .  .  lect  about  desmids,  diatoms,  and  other  microscopic 
plants,  in  a  lighted  preparation,  in  the  same  way 
as  about  air  bubbles  (Fig.  25).  Many  other  bac- 
teria react  in  the  same  way  to  oxygen;  notably 
the  ordinary  bacterium  of  decaying  vegetable 
infusions,  Bacterium  termo.  Bacteria  react  to  ex- 
ceedingly minute  quantities  of  oxygen,  so  that  it 
is  possible  to  use  them  as  tests  for  the  presence  of 
small  amounts  of  this  substance.  Engelmann 
calculates  that  a  bacterium  may  react  to  one  one- 
hundred-billionth  of  a  milligram  of  oxygen.  By 
means  of  such  reactions  he  has  carried  on  investi- 
gations to  determine  whether  various  green  or  col- 
orless organisms  do  or  do  not  give  off  oxygen ; 
results  may  be  attained  in  this  way  that  could 
scarcely  be  reached  otherwise  (Fig.  26).  Spirillum 
(especially  S.  tenue)  is  so  remarkably  sensitive  to 
oxygen  that  many  individuals  may  react  to  the 
oxygen  produced  by  a  single  specimen  of  another 
smaller  bacterium  (Engelmann). 

When  bacteria  collect  about  bubbles  or  near 
the  edge  of  the  cover-glass  as  a  reaction  to  oxy- 


Fig.  26.  — An  experi- 
ment of  Engelm ann  ( 1 894), 
showing  that  when  a  di- 
atom is  partly  lighted,  only 
the  part  exposed  to  the 
light  produces  oxygen. 
The  upper  half  of  the  di- 
atom was  in -the  shade,  the 
lower  half  in  the  light. 
The  bacteria  have  gathered 
only  about  the  lighted  half 
of  the  diatom. 


THE  BEHAVIOR   OF  BACTERIA 


31 


gen,  certain  differences  are  to  be  observed  in  different  species.  Spirilla 
usually  gather  in  a  narrow  zone  a  short  distance  from  the  air  surface, 
while  Bacterium  termo  and  most  other  species  collect  in  another  zone, 
a   little  closer  to  the  air.     These  relations  are  illustrated  for  Spirilla 


and  certain  infusoria  in  Fig. 
reversal  of  movement  is 
brought  about  in  two  differ- 
ent regions.  Passage  from 
the  zone  in  which  the  quan- 
tity of  oxygen  is  adapted  to 
the  particular  species,  to  a 
region  having  less  oxygen, 
causes  the  reversal;  passage 
to  a  region  having  more  oxy 


In  such  cases  it  is  found  that  the 


i' 

>N' 

...  l('i v*i-'r-JiV,, ... 

•J' 

1 

1  //                \\^ 

i*.' 

% 

§•     *    /                                \     ^ 

S 

I 
| 

b~ 

H\       )}i 

.2 

.-■.• 
** 

a 

a 

Fig.  27. —  Collections  of  Spirilla,  a,  and  a  ciliate  in- 


o-pn   (next  to  the   air   surfaced    fusorian  Anophrys,  b,  at  the  corner  of  the  cover-glass, 
gen   (nexi  to    tne   dir   bUridLC;    and  about  a  bubble      Each  remains  in  a  narrow  zone 

Causes  the  reversal  with  even    a  certain  distance  from    the  air   surface,  the  bacteria 

a  farther  away  than  the  infusoria.     After  Massart. 

greater  precision.     As  a  re-  ' 

suit,   each  species  remains  swimming  about  within  the  narrow  zone 

adapted  to  it,  at  a  short  distance  from  the  air. 

Thus  any  given  species  is  adapted  to  a  certain  concentration  of  oxy- 
gen, which  may  be  called  its  optimum.  Passage  from  the  optimum  in 
either  direction  —  toward   more   oxygen   or  less   oxygen  —  causes   the 

reversal    of    movement,    so    that    the 
bacteria  remain  in  the  optimum. 

Oxygen  is  of  course  necessary,  or 
at  least  useful,  to  these  bacteria ;  most 
of  them  become  immobilized  soon  if 
oxygen  is  excluded  from  the  water. 
The  reversal  of  movement  on  passing 

'^M^- '-•'•'•'•.'•'  to  a  regi°n  °f  less  oxygen  is  thus  an 

•:£§||p ;  :'.'•   ••'•  .'■' •'•  adaptive  reaction.     It  is  probable  that 

••..;';.    ^r'  •■'"'  •'■.  ;'•;-.'••■ .'  the  concentration  in  which  each  spe- 

'■'.  ■■:■:'■■'■ :  V  V:  •*•' '  ' ''  cies    tends    to    remain    is    that    most 

favorable  to  its  life  activities.     Some 

Fig.  28.  — Collection  of   Chromatium  ...  111  j.  • 

wdssii  in  and  about  a  capillary  tube  con-    bacteria   (the  so-called  anaerobic  spe- 

taining  0.3   per  cent  ammonium  nitrate.     cJes)  ^Q  not  require  OXVgen,  and  these 
After  Miyoshi  (1897).  '     .  ?        11      /• 

bacteria  do  not  collect  in  an  oxygen- 
ated area.  One  of  these,  Amylobacter,  is  known  to  avoid  oxygen  in 
all  effective  concentrations;  that  is,  it  reverses  its  movement  on  com- 
ing to  a  region  containing  oxygen  (Rothert,  iqoi). 

Many  bacteria  collect  in  various  other  chemicals  in  the  same  manner 
as  in  solutions  of  oxygen  (see  Fig.  28).     Such  collections  are  usually 


32  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

formed  in  food  substances ;  meat  extract,  for  example,  is  an  agent  which 
produces  such  collections  in  most  species  of  bacteria.  Pfeffer  (1884) 
found  that  Bacterium  termo  forms  collections  in  meat  extract,  aspara- 
gine,  peptone,  white  of  egg,  conglutin,  grass  extract,  leucin,  urea,  and 
various  other  substances  which  might  serve  as  nourishment.  The 
so-called  sulphur  bacteria  use  hydrogen  sulphide  in  their  nutritive  pro- 
cesses, and  are  found  to  collect  in  solutions  of  this  substance  (Miyoshi, 
1897). 

Many  bacteria  collect  also  in  solutions  of  chemicals  which  probably 
do  not  serve  directly  as  food.1  Bacterium  termo  collects  markedly  in 
weak  solutions  of  potassium  carbonate,  so  that  this  is  a  favorable  sub- 
stance for  demonstrating  the  collections.  It  collects  also  in  most  salts 
of  potassium,  and  in  a  less  marked  way  in  many  other  inorganic  chem- 
icals. Indeed,  this  species  may  be  said  to  gather  in  weak  solutions  of 
most  inorganic  chemicals,  save  in  those  of  the  powerful  acids  and  alka- 
lies. This  bacterium  lives  on  decaying  vegetation,  from  which  many 
chemicals  diffuse  into  the  surrounding  water ;  potassium  salts  especially 
are  given  off  in  this  manner.  The  tendency  of  the  organisms  to  collect 
in  such  salts  therefore  keeps  them  in  proximity  to  the  decaying  vegeta- 
tion which  serves  them  as  nourishment ;  these  reactions  are  thus  indi- 
rectly adaptive.  But  Bacterium  termo  collects  in  certain  chemicals  that 
are  not  thus  given  off  by  decaying  vegetation.  Pfeffer  (1888)  found  that 
they  gather  in  salts  of  rubidium,  caesium,  lithium,  strontium,  and 
barium,  with  which  under  natural  conditions  they  never  come  in  con- 
tact. It  has  been  suggested  that  this  may  be  explained  as  due  to  a  simi- 
larity in  the  effect  of  these  chemicals  to  the  effects  of  others  which  they 
do  meet  under  natural  conditions.  The  organisms  react  thus  in  the 
same  way  to  similar  stimulation,  without  regard  to  its  diverse  source  in 
different  cases. 

Many  other  bacteria  resemble  Bacterium  termo  in  collecting  in  solu- 
tions of  a  great  variety  of  chemicals.  Miyoshi  (1897)  found  that  the 
sulphur  bacterium  Chromatium  weissii  forms  collections  in  weak  solu- 
tions of  hydrogen  sulphide,  potassium  nitrate,  ammonium  nitrate  (Fig. 
28),  calcium  nitrate,  sodium-potassium  tartrate,  ammonium  phosphate, 
monosodium  phosphate,  sodium  chloride,  cane  sugar,  grape  sugar, 
asparagine,  and  peptone. 

Some  reactions  can  hardly  be  considered  in  any  way  adaptive. 
Rothert  (1901)  found  that  Amylobacter  and  another  bacterium  collect 

1  The  method  of  testing  the  reaction  to  chemicals  has  usually  been  as  follows.  A  capillary 
glass  tube  is  filled  with  the  solution  to  be  tested,  and  one  end  is  sealed.  The  open  end  is 
then  brought  into  the  fluid  containing  bacteria  ;  these  then  enter  the  tube  (Fig.  28)  or  leave 
it  empty  (Fig.  24,  .-/),  depending  on  their  reaction  to  the  chemical. 


THE  BEHAVIOR   OF   BACTERIA  33 

in  weak  solutions  of  ether.  From  the  method  by  which  the  gatherings 
are  produced,  it  is,  of  course,  evident  that  collection  in  any  agent  signi- 
fies merely  that  the  organisms  are  less  repelled  by  this  agent  than  by 
the  surrounding  conditions.  All  such  collections  are  doubtless  to  be 
conceived  as  brought  about  by  a  reversal  of  the  movement  on  passing 
from  the  dilute  chemical  to  water  containing  none  of  the  chemical.  In 
many  cases  this  has  been  determined  by  direct  observations ; x  in  other 
cases  the  observations  have  not  been  made. 

If  the  chemical  is  stronger,  the  reversal  of  movement  is  produced 
when  the  bacteria  come  in  contact  with  it,  so  that  strong  chemicals  as 
a  rule  remain  empty.  Thus  the  same  chemicals  that,  when  dilute,  pro- 
duce a  "positive  reaction"  cause,  when  stronger,  a  negative  reaction. 
All  substances  in  dilute  solutions  of  which  Spirillum  gathers  are  avoided 
if  stronger  solutions  are  used.  Miyoshi  found  this  to  be  true  also  for 
Chromatium  iveissii;  and  it  is  indeed  a  general  rule  for  bacteria. 

Why  should  the  bacteria  avoid  strong  solutions  of  the  very  substances 
that  when  weak  are  "attractive"?  It  is,  of  course,  well  known  that 
strong  solutions  are  as  a  rule  injurious;  the  negative  reaction  is  there- 
fore distinctly  adaptive  under  these  conditions.  Even  when  we  can  see 
no  use  for  the  positive  reaction,  as  in  the  case  of  the  collecting  of  Amylo- 
bacter  in  a  solution  of  ether,  we  find  that  the  reaction  becomes  negative 
as  soon  as  the  solution  becomes  injurious.  Amylobacter  keeps  out  of 
stronger  solutions  of  ether. 

Yet  the  bacteria  are  no  more  infallible  in  detecting  injurious  sub- 
stances than  are  higher  organisms.  If  a  poisonous  chemical  is  mixed 
with  a  solution  in  which  the  bacteria  naturally  collect,  the  organisms  may 
continue  to  enter  a  drop  of  the  solution,  where  they  are  killed.  So 
Pfeffer  (1888,  p.  628)  found  that  if  to  an  attractive  solution  of  0.019  Per 
cent  potassium  chloride  be  added  0.0 1  per  cent  mercuric  chloride,  Bac- 
terium termo  and  Spirillum  undula  continue  to  pass  into  the  solution, 
though  they  are  there  immediately  killed.  Bacterium  termo  swarms  into 
solutions  of  morphine  (morphium  chloride),  where  after  ten  minutes  to 
an  hour  all  motion  ceases. 

To  just  what  action  of  the  strong  solution  is  the  repellent  effect, 
when  it  occurs,  due?  Strong  solutions  may  be  injurious  from  two  dif- 
ferent classes  of  causes.  The  specific  properties  of  the  given  chemical 
may  cause  injuries  when  acting  intensely,  and  this  might  induce  the 
negative  reaction.  But  farther,  in  any  strong  solution  the  osmotic  press- 
ure is  high,  and  this  produces  injury  in  organisms  by  withdrawing  the 


1  The  reversal  of  motion  under  these  circumstances  has  been  described  especially  by 
Pfeffer  (1884),  Rothert  (1901),  and  Jennings  and  Crosby  (1901). 

D 


34 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


water  from   the   protoplasm    (plasmolysis).     The  reaction  of  bacteria 
might  then  be  due  to  this  physical  effect  of  strong  solutions. 

If  the  repellent  effects  of  strong  chemicals  are  due  to  their  osmotic 
pressure,  then  all  solutions  having  equal  osmotic  pressure  must  be 
equally  repellent.  This  gives  a  method  of  testing  the  matter.  Bacteria 
have  been  subjected  to  the  action  of  many  chemicals  in  solutions  of 
equivalent  osmotic  pressure,  with  the  following  results.  There  are  many 
strong  chemicals  which  cause  reaction  when  the  osmotic  pressure  is  very 
low,  —  much  lower  than  in  the  weakest  solutions  required  to  produce 
reaction  in  other  substances.  Such  are,  as  a  rule,  the  strong  mineral 
acids  and  alkalies  (Pfeffer) ;  such  are  potassium  cyanide,  potassium 
oxalate,  sodium  carbonate,  sodium  sulphite,  and  potassium  nitrate  in 
the  experiments  of  Massart  (1889).  The  reactions  produced  by  these 
substances  can  be  due  then  only  to  their  chemical  effects,  without  re- 
gard to  the  osmotic  pressure.  On  the  other  hand,  Massart  has  shown 
that  in  two  species  of  bacteria  —  Spirillum  undula  and  Bacterium  me- 
gatherium —  the  repellent  power  of  a  large  number  of  chemicals  is  pro- 
portional to  the  osmotic  pressure  of  the  solutions.     It  appears  probable 

therefore  that  the  osmotic  press- 
ure is  the  cause  of  the  reaction.1 
In  certain  other  bacteria  it  has 
been  demonstrated  that  there 
is  no  such  sensitiveness  to  os- 
motic pressure.  Bacterium  termo 
enters  the  strongest  solutions  of 
attractive  salts.  This  is  sup- 
posed to  be  because  its  proto- 
plasm is  permeable  to  the  salts 
in  question.  Taken  all  together, 
the  experimental  results  demon- 
strate that  in  many  cases  the 
negative  reaction  is  due  to  the 
chemical  properties  of  the  sub- 
stance, and  they  render  it  probable  that  in  some  other  cases  the  reaction 
is  due  to  the  osmotic  pressure. 

It  is  not  always  more  concentrated  solutions  that  cause  the  reversal 
of  movement.     Bacteria  that  live  in  sea  water  keep  out  of  areas  of  dis- 


Fig.  29.  —  Repulsion  of  Spirilla  of  sea  water 
by  distilled  water.  The  upper  drop  consists  of 
sea  water  containing  Spirilla;  the  lower  of  distilled 
water.  At  x  these  have  just  been  united  by  a 
narrow  neck.  At  y  and  z  the  bacteria  are  driven 
back  before  the  advancing  distilled  water.  After 
Massart  (1891). 


1  This  conclusion  is  weakened  by  the  fact  that  the  bacteria  are  much  less  repelled  by  sev- 
eral substances  —  glycerine,  asparagine,  dextrose,  and  saccharose  —  even  when  they  are  so 
concentrated  as  to  have  higher  osmotic  pressure  than  the  repellent  solutions  of  the  substances 
above  mentioned  (  Massart,  1889).  This  is  explicable  only  by  making  certain  special,  un- 
proved assumptions  for  each  case.     The  matter  needs  further  investigation. 


THE  BEHAVIOR   OF  BACTERIA  35 

tilled  water  in  the  same  way  (Fig.  29).  This  result  may  be  due  to  the 
fact  that  the  osmotic  pressure  of  the  distilled  water  is  less  than  that  of 
the  sea  water.  On  the  other  hand,  it  is  possible  that  it  is  due  merely  to 
the  cessation  of  the  chemical  action  of  certain  components  of  the  sea 
water.  The  case  would  then  be  comparable  to  the  reaction  induced 
when  bacteria  come  to  a  region  containing  no  oxygen,  as  described  in 
the  preceding  pages. 

Most  bacteria  do  not  react  to  light.  But  there  are  certain  bacteria 
for  whose  successful  development  light  is  required,  and  in  these  species 
we  find  that  reaction  to  light  occurs  in  the  same  manner  as  the  reaction 
to  oxygen  in  others.  The  species  which  react  to  light  belong  chiefly  to 
the  group  of  sulphur  bacteria.  They  contain  a  purple  coloring  matter 
(bacterio-piirpurin),  which  acts  in  a  manner  analogous  to  the  chlorophyl 
of  higher  plants.  By  its  aid,  through  the  agency  of  light,  these  bacteria 
break  up  and  assimilate  carbon  dioxide,  giving  off  oxygen. 

Engelmann  (1882  a,  1888)  made  a  thorough  study  of  the  relations  to 
light  in  one  of  these  bacteria,  Chromatium  photometricum  (Fig.  23,  b). 
This  organism  moves  actively  and  develops  well  in  diffuse  light,  but  in 
the  dark  movement  soon  ceases  and  development  stops.  Only  in  the 
light  does  it  assimilate  carbon  dioxide  and  give  off  oxygen.  In  corre- 
spondence with  this,  Chromatium  photometricum  collects  in  lighted  areas. 
This  takes  place  in  the  same  manner  as  the  collection  of  bacteria  in  oxy- 
gen. Engelmann  placed  the  bacteria  on  a  glass  slide,  in  the  usual  way, 
then  illuminated  a  certain  spot  from  below,  while  light  was  cut  off  from 
the  remainder  of  the  preparation.  He  found  that  the  bacteria  do  not 
react  on  entering  the  lighted  area.  But  when  once  within  this  area,  on 
coming  to  the  outer  boundary  they  suddenly  reverse  their  movement 
and  swim  backward  a  distance.  Then  they  start  forward  again;  on 
coming  anew  to  the  boundary  they  react  as  before,  and  this  happens 
every  time  they  reach  the  confines  of  the  lighted  area.  Thus  none  leave 
the  light ;  all  those  that  enter  the  lighted  area  remain,  and  a  dense  col- 
lection is  soon  formed  here.  In  every  detail  the  phenomena  are  parallel 
to  those  found  in  the  reactions  of  other  bacteria  to  oxygen,  as  described  in 
previous  pages. 

A  sudden  decrease  of  light  causes  the  same  backward  movement  that 
is  observed  when  the  bacteria  come  to  the  edge  of  the  lighted  area.  If 
the  light  is  suddenly  decreased  by  closing  the  diaphragm  of  the  micro- 
scope, all  the  bacteria  at  once  swim  backward  a  distance,  —  often  ten 
to  twenty  times  their  length.  This  shows  that  the  reaction  is  not  due 
to  the  difference  in  illumination  of  two  ends  or  two  sides  of  the  organism, 
but  only  to  the  sudden  decrease  in  light.  This  is  shown  also  by  the  fact 
that  the  bacteria  may  swim  completely  across  the  boundary  of  the  lighted 


36 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


region  into  the  dark  before  reacting;  the  reaction  then  carries  them 
back  into  the  light.  With  the  smaller  bacteria  the  reaction  usually 
occurs  in  this  manner,  while  in  larger  species  (Monas  okeni;  Ophido- 
monas  sanguined)  the  reversal  of  movement  occurs  when  only  one  end 
has  passed  into  the  dark.  A  sudden  increase  of  light  merely  causes  the 
organisms  to  swim  forward  a  little  more  rapidly. 

The  purple  bacteria  are  sensitive  in  different  degrees  to  lights  of  dif- 
ferent colors,  tending  to  gather  in  certain  colors  more  than  in  others. 
This  is  shown  in  a  most  striking  way  when  a  spectrum  is  thrown  on  a 
preparation  of  Chromatium  photometricum  (Fig.  30).     The  largest  num- 


1 

ft 

■ 

1 , 
*     ,*  •  • 

.•     .... 

1 

• 
•         • 

•  •    *        ■    • 

•    ■  • 

•  <                    • 

1 

H 

K 

:       i 

3            i 

>         / 

5                                       g 

Fig.  30.  —  Distribution  of  bacteria  in  a  microscopic  spectrum.  The  largest  group  is  in  the 
ultra-red,  to  the  left;  the  next  largest  group  in  the  yellow-orange,  close  to  the  line  D.  After 
Engelmann. 


ber  of  the  bacteria  collect  in  the  ultra-red  rays,  which  do  not  affect  the 
human  eye  at  all.  There  is  another  collection  in  yellow-orange,  while 
a  few  are  scattered  through  the  green  and  blue.  None  are  found  in  the 
red,  the  violet,  or  ultra-violet.  These  collections  arise  in  the  same  man- 
ner as  those  in  the  white  light.  Bacteria  swimming  from  blue  toward 
yellow-orange,  or  from  red  toward  ultra-red,  do  not  react  at  all,  but  con- 
tinue their  course.  But  specimens  swimming  in  the  opposite  direction 
react  in  the  usual  way,  by  leaping  back,  when  they  come  to  the  outer 
boundary  of  the  ultra-red  or  the  orange-yellow.  Hence,  in  the  course  of 
time,  if  the  bacteria  continue  moving,  almost  all  of  them  will  be  found 
in  the  two  regions  last  named. 

It  is  a  most  interesting  fact  that  the  colors  in  which  the  bacteria  col- 
lect are  exactly  those  which  are  most  absorbed  by  them,  and  are  also 
those  which  are  most  favorable  to  their  metabolic  processes.  Engel- 
mann showed  that  most  oxygen  is  given  off,  and  hence  that  most  carbon 
dioxide  is  assimilated,  in  the  ultra-red  rays,  while  next  to  the  ultra-red 
the  orange-yellow  are  most  favorable  to  these  processes.  The  reactions 
of  these  bacteria  to  light  are  therefore  adapted  with  remarkable  preci- 
sion to  bringing  them  into  regions  which  offer  the  best  conditions  for 
their  development.     This  is  the  more  remarkable  when  we  consider  that 


THE  BEHAVIOR   OF  BACTERIA  37 

under  natural  conditions  the  bacteria  rarely  if  ever  have  opportunity 
to  react  to  the  separated  spectral  colors. 

Besides  the  purple  bacteria,  a  green  form,  Bacterium  chlorinum,  is 
known  to  assimilate  carbon  dioxide  and  to  collect  in  light,  in  the  same 
manner  as  do  the  purple  species. 

The  precise  method  by  which  bacteria  react  to  heat  and  cold  has 
been  little  studied.  Mast  (1903)  has  shown  that  Spirilla  do  not  react 
at  all  to  changes  in  temperature.  If  a  portion  of  the  preparation  con- 
taining them  is  heated,  they  continue  to  pass  into  this  region  just  as 
before,  though  they  may  be  at  once  killed  by  the  heat.  They  may  pass 
also  into  a  cold  region,  where  motion  gradually  ceases. 

The  reaction  to  the  electric  current,  like  that  to  heat  and  cold,  is  in 
need  of  a  thorough  examination.  Verworn  found  that  when  subjected 
to  a  continuous  current  some  bacteria  pass  to  the  anode,  others  to  the 
cathode. 

When  placed  in  a  vertical  tube,  some  kinds  of  bacteria  pass  upward 
to  the  top,  in  opposition  to  the  force  of  gravity,  while  others  gather  at 
the  lower  end  (Massart,  1891).  The  factors  on  which  this  reaction  to 
gravity  depends,  and  the  precise  way  in  which  the  reaction  takes  place, 
are  unknown. 

Bacteria  often  react  to  contact  with  solids  by  settling  down  and 
becoming  quiet  on  the  surface  of  the  solid,  which  is  usually  some  food 
body.  Bacterium  termo  thus  forms  dense  collections  on  the  surface  of 
such  an  object  as  a  fly's  leg. 

3.   General  Features  in  the  Behavior  of  Bacteria 

We  find  that  the  chief  reactions  of  bacteria,  so  far  as  they  have  been 
precisely  determined,  take  place  through  a  single  movement,  —  a  tem- 
porary reversal  of  the  direction  of  swimming.  This  reaction  is  so  simple 
as  to  be  comparable  to  a  reflex  action  as  we  find  it  in  an  isolated  muscle. 
Whether  the  bacteria  collect  in  a  certain  region  or  avoid  it  depends  on 
what  it  is  that  produces  this  reversal  of  movement.  The  reaction  is 
caused  as  a  rule  by  a  change  in  the  environment  of  the  organism.  This 
change  is  usually  brought  about  by  the  movement  of  the  bacterium  into 
a  region  differing  from  that  which  it  previously  occupied,  but  it  may  be 
due  to  an  active  alteration  of  the  environment,  as  when  light  is  suddenly 
cut  off.  For  the  reaction  to  occur  with  the  result  of  a  general  movement 
of  the  organisms  into  a  certain  region,  it  is  not  necessary  that  different 
parts  of  the  body  should  be  differently  stimulated,  as  we  found  to  be  the 
case  in  Amoeba.  The  only  requirement  for  producing  a  general  move- 
ment of  the  organisms  in  a  certain  direction  is  that  movement  in  any  other 


38  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

direction  shall  result  in  such  a  change  as  will  produce  the  reversal  of 
movement.  Not  every  change  in  the  environment  produces  a  reaction. 
A  change  leading  toward  a  certain  optimum  condition  produces  no  reac- 
tion, while  a  change  of  opposite  character  causes  the  reversal  of  move- 
ment. A  negative  change  in  the  environment  —  the  decrease  or  cessa- 
tion of  action  of  a  certain  agent  —  may  be  as  effective  a  stimulus  as  is 
a  positive  change  due  to  the  entrance  of  a  new  agent  into  action.  This 
is  well  illustrated  in  the  reactions  to  light  and  oxygen.  All  these  rela- 
tions we  shall  meet  again,  more  fully  illustrated,  in  the  behavior  of 
infusoria. 

The  strength  of  the  change  necessary  to  cause  a  reaction  has  been 
found  by  Pfeffer  to  vary  in  accordance  with  Weber's  law.  This  as  usually 
formulated  expresses  certain  relations  between  sensation  and  stimulus 
in  man.  According  to  this  law,  it  is  the  relative  change  in  the  environ- 
ment, not  the  absolute  change,  that  causes  a  perceptible  difference  in 
sensation.  Thus  if  a  certain  perceptible  weight  x  is  pressing  on  the  skin 
of  certain  parts  of  the  body,  it  requires  an  additional  weight  of  about  ^  x 
to  produce  a  noticeable  difference  in  the  sensation ;  if  the  original  weight 
is  2  x,  then  an  additional  weight  of  f  x  is  required.  In  general  the  addi- 
tional weight  must  be  about  one-third  the  original  one  before  a  notice- 
able difference  in  sensation  is  produced.  In  the  bacteria  we  know  noth- 
ing about  sensations,  but  if  we  substitute  reaction  for  sensation,  similar 
relations  are  found  to  hold  good.  Pfeffer  found  that  if  Bacterium  termo 
is  cultivated  in  o.oi  per  cent  meat  extract,  they  collect  noticeably  in  capil- 
lary tubes  containing  0.05  per  cent  meat  extract,  but  not  in  a  weaker 
solution.  For  producing  reaction  the  inner  fluid  must  therefore  be  five 
times  as  strong  as  the  outer.  If  now  the  culture  fluid  is  raised  to  a 
strength  of  0.1  per  cent  meat  extract,  then  five  times  this  strength  — 
namely,  0.5  per  cent  —  is  required  to  induce  the  bacteria  to  collect.  If 
the  culture  fluid  is  1  per  cent,  the  fluid  in  the  capillary  tube  must  be 
5  per  cent  in  order  to  produce  the  usual  reaction.  The  fluid  in  which  the 
bacteria  collect  must  be  always  five  times  as  strong  as  that  in  which 
they  live.  It  is  the  relative  change,  not  the  absolute  change,  that  in- 
duces reaction.  This  agreement  between  the  relation  of  sensation  to 
stimulus  in  man  and  that  of  reaction  to  stimulus  in  these  low  organisms 
is  of  great  interest. 

There  is  a  considerable  amount  of  variation  in  the  reactions  among 
different  individuals  of  the  same  species.  Thus,  Rothert  found  that 
specimens  of  Amylobacter  from  a  certain  culture  were  markedly  negative 
to  oxygen  and  positive  to  ether,  while  in  specimens  from  another  culture 
these  reactions  were  hardly  observable.  Even  among  individuals  of  the 
same  culture  there  is  variation.     Engelmann  found  that  when  the  light 


THE  BEHAVIOR   OF  BACTERIA  39 

falling  on  a  group  of  individuals  of  Chromatium  was  suddenly  decreased, 
a  few  react  to  even  very  slight  changes,  a  larger  number  to  more  consid- 
erable changes,  while  some  hardly  react  at  all.  "Nervous"  and  "apa- 
thetic" individuals,  Engelmann  says,  can  be  distinguished  in  any  group. 
Even  in  the  same  individual  the  reaction  may  vary.  Engelmann  found 
that  if  the  light  was  suddenly  decreased,  then  restored,  and  at  once  de- 
creased again,  the  bacteria  usually  do  not  react  to  the  second  decrease, 
though  they  did  to  the  first. 

Among  different  kinds  of  bacteria  there  are,  as  we  have  seen,  certain 
constant  differences  in  the  reactions.  A  relation  of  great  significance 
becomes  evident  on  examining  the  facts;  behavior  under  stimulation 
depends  on  the  nature  0}  the  normal  life  processes,  —  especially  the  meta- 
bolic processes.  Bacteria  that  require  oxygen  in  their  metabolism  col- 
lect in  water  containing  oxygen ;  bacteria  to  which  oxygen  is  useless  or 
harmful  avoid  oxygen.  Bacteria  that  use  hydrogen  sulphide  in  their 
metabolism  gather  in  that  substance.  Bacteria  that  require  light  for 
the  proper  performance  of  their  metabolic  processes  gather  in  light, 
while  others  do  not.  When  one  color  is  more  favorable  than  others  to 
the  metabolic  processes  the  bacteria  gather  in  that  color,  even  though 
they  may  under  natural  conditions  have  no  experience  with  separated 
spectral  colors.  Keeping  in  mind  that  all  these  collections  are  formed 
through  the  fact  that  the  organisms  reverse  their  movement  at  passing 
out  of  the  favorable  conditions,  these  relations  can  be  summed  up  as 
follows :  Behavior  that  results  in  interference  with  the  normal  metabolic 
processes  is  changed,  the  movement  being  reversed,  while  behavior  that 
does  not  result  in  interference  or  that  favors  the  metabolic  processes  is 
continued. 

This  statement  doubtless  does  not  express  the  behavior  completely, 
yet  the  general  fact  which  it  sets  forth  is  on  the  whole  clearly  evident. 
The  result  of  this  method  of  action  is  to  make  the  behavior  regulatory, 
or  adaptive.  Through  it,  the  bacteria,  like  higher  organisms,  avoid 
injurious  conditions  and  collect  in  beneficial  ones.  There  are  some 
exceptions  to  this ;  the  adaptiveness  is  not  perfect,  as  nothing  is  perfect 
under  all  conditions.  The  exceptions  are  perhaps  not  more  numerous 
in  these  lowest  organisms  than  in  the  highest  ones. 

Putting  all  together,  the  behavior  of  the  bacteria  may  be  summed  up 
as  follows :  They  swim  about  in  a  direction  determined  by  the  posi- 
tion of  the  body  axis,  until  the  movement  subjects  them  to  an  unfavora- 
ble change ;  thereupon  they  reverse  and  swim  in  some  other  direction. 
With  rapid  movements  and  much  sensitiveness  to  unfavorable  influ- 
ences, this  soon  results  in  their  finding  and  remaining  in  the  favorable 
regions.     In  the  presence  of  a  localized  region  of  favorable  conditions 


40  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

(food  or  oxygen,  for  example)  the  organisms  do  not  show  movement  in 
a  single  direction,  adapted  to  reaching  these  favorable  conditions.  On 
the  contrary,  they  show  movements  in  all  sorts  of  directions;  one  of 
these  is  finally  continued  or  selected  by  its  success.  We  find  again  be- 
havior based  on  the  "selection  from  among  the  conditions  produced  by 
varied  movements." 

LITERATURE   II 

(On  the  behavior  of  Bacteria) 

Engelmann,  1881,  1882  a,  1888.  1894;  Jennings  and  Crosby,  1901 ;  Massart, 
1889,  1891,  1891a;  Mast,  1903;  Miyoshi,  1897;  Pfeffer,  1884,  1888;  Rothert, 
1901,  1903. 


CHAPTER   III 
THE   BEHAVIOR   OF    INFUSORIA;    PARAMECIUM 

Structure;  Movements;  Method  of  Reaction  to  Stimuli 

introductory 

The  name  Infusoria  is  applied  to  those  unicellular  organisms  (aside 
from  bacteria)  that  swim  by  means  of  cilia  or  flagella,  as  well  as  to  a  few 
others.  The  organs  of  locomotion  are  protoplasmic  processes  on  the 
body  surface.  Where  these  are  short  and  numerous,  they  are  called 
cilia;  where  they  are  long  and  the  organism  bears  but  one  or  a  small 
number,  they  are  called  flagella.  The  organisms  bearing  cilia  are 
classed  together  as  Ciliata ;  those  with  flagella  are  the  Flagellata.  Fig- 
ure 31  shows  a  number  of  characteristic  forms  of  the  Ciliata.  Along  with 
the  infusoria  we  shall  take  up  other  unicellular  organisms  or  develop- 
mental stages  that  swim  by  means  of  such  protoplasmic  processes,  — 
for  example,  spermatozoa  and  swarm   spores. 

The  infusoria  are  commonly  found,  as  the  name  implies,  in  infusions 
of  decaying  animal  and  vegetable  matter.  One  of  the  commonest  and  best 
known  of  the  infusoria  is  Paramecium,  found  in  water  containing  de- 
caying marsh  plants,  or  in  hay  infusion  with  which  some  marsh  or  pond 
water  has  been  mixed.  The  behavior  of  Paramecium  has  been  studied 
more  than  that  of  any  other  infusorian,  so  that  we  shall  take  this  up 
first  as  a  representative  of  the  group.  The  behavior  of  other  species 
will  be  then  examined  to  discover  how  far  the  relations  in  Paramecium 
are  typical,  and  to  bring  out  differences  —  especially  points  for  which 
Paramecium  is  not  a  favorable  object  of  study. 


1.   Behavior  of  Paramecium;  Structure 

Paramecium  (Fig.  32)  is  a  whitish,  cigar-shaped  animal,  living  in 
immense  numbers  in  decaying  vegetable  infusions,  and  visible  to  the 
naked  eye  as  a  minute,  elongated  particle.     The  anterior  part  of  the 

41 


42 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


body  is  slender  but  blunt,  the  posterior  part  thicker,  but  more  pointed. 
Thus  the  two  ends  differ,  as  in  some  bacteria,  and  there  is  a  further 


Fig.  31.  —  Examples  of  ciliate  infusoria,  a,  Spirostomum  ambiguum  Ehr.,  after  Stein. 
b,  Slentor  roeselii  Ehr.,  after  Stein,  c.  Vorticella  nebulifera  O.  F.  M.,  after  Biitschli.  d,  Col- 
pidium  colpoda  Ehr.,  after  Schewiakoff,  from  Biitschli.  e,  Loxophyllum  meleagris  O.  F.  M., 
after  Biitschli.     /,  Stylonychia  mytilus    Ehr.,  after  Engelmann. 


differentiation  of  the  lateral  surfaces.     One  side,  the  oral  surface,  bears 
a  broad,  oblique  groove,  known  as  the  oral  groove,  or  peristome,  ex- 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


43 


tending  from  the  mouth  in  the  middle  of  the  body  forward  to  the  anterior 
end.  When  the  animal  is  placed  with  the  oral  surface  below,  the  groove 
extends  from  the  right  behind 
toward  the  left  in  front  (see  Fig. 
32).  The  animal  is  thus  not  bi- 
laterally symmetrical,  but  slightly 
spiral  in  form.  The  surface  oppo- 
site the  oral  groove  is  marked  by 
the  presence  near  it  of  two  large 
contractile  vacuoles ;  this  may  be 
called  the  aboral  surface.  By  con- 
sidering the  oral  surface  as  ventral 
we  may  distinguish  for  convenience 
right  and  left  sides.  The  entire 
body  is  covered  with  fine  cilia,  set 
in  oblique  rows.  Those  at  the  pos- 
terior end  are  a  little  longer  than 
the  others. 

As  to  internal  structure,  we  may 
distinguish  an  outer  firm  layer 
known  as  the  ectosarc,  enclosing 
an  inner  fluid  portion,  the  endo- 
sarc.  The  ectosarc  is  covered  by 
a  thin  outer  cuticle;  below  this  it 
is  thickly  set  with  rodlike  sacs, 
placed  perpendicular  to  the  surface 
and  known  as  trichocysts ;  the  con- 
tents of  these  may  be  discharged  as 
fine  threads.  The  endosarc  con- 
tains two  nuclei,  the  large  macronu- 

cleus  and  the  minute  mirrormrleim     food   vacuoles;   8>  Sullet''   w>  mouth; 
Cieus  dna  me   mmuie  micronUCieUS,     maCronucleus ;    mi.,  micronucleus;  o.g.,  oral 

together  with  numerous  masses  of  groove;  P.,  pellicle;  tr.,  trichocyst  layer. 
f^^A      w.^f     „f     +1-.^™      „~„l~„„J     ;„     The  arrows  show  the  direction  of  movement 

food,    most    of    them    enclosed    m    Qf  the  food  vacuoles, 
vacuoles  of   water.     The  endosarc 

is  in  continual  movement,  rotating  lengthwise  of  the  body,  in  the 
direction  shown  by  the  arrows  in  Fig.  32.  Between  endosarc  and 
ectosarc,  but  attached  to  the  latter,  are  the  two  contractile  vacuoles, 
which  at  intervals  collapse,  emptying  their  contents  to  the  outside. 
From  the  mouth  (m)  a  passageway  the  gullet  (g),  leads  through  the 
ectosarc  into  the  endosarc. 


Fig.  32.  —  Paramecium,  viewed  from  the 
oral  surface.  L,  left  side;  R,  right  side. 
an.,  anus;  ec,  ectosarc;  en.,    endosarc;    j.v., 

ma., 
macronucleus; 


44 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


2.  Movements 


Paramecium  swims  by  the  beating  of  its  cilia.     These  are  usually 

inclined  backward,  and  their  stroke  then  drives 
the  animal  forward.  They  may  at  times  be  di- 
rected forward ;  their  stroke  then  drives  the  ani- 
mal backward.  The  direction  of  their  effective 
stroke  may  indeed  be  varied  in  many  ways,  as 
we  shall  see  later.  The  stroke  of  the  cilia  is 
always  somewhat  oblique,  so  that  in  addition  to 
its  forward  or  backward  movement  Paramecium 
rotates  on  its  long  axis.  This  rotation  is  over  to 
the  left  (Fig.  33),  both  when  the  animal  is  swim- 
ming forward,  and  when  it  is  swimming  back- 
ward. The  revolution  on  the  long  axis  is  not 
due  to  the  oblique  position  of  the  oral  groove,  as 
might  be  supposed,  for  if  the  animal  is  cut  in 
two,  the  posterior  half,  which  has  no  oral  groove, 
continues  to  revolve. 

The  cilia  in  the  oral  groove  beat  more  effec- 
tively than  those  elsewhere.  The  result  is  to 
turn  the  anterior  end  continually  away  from  the 
oral  side,  just  as  happens  in  a  boat  that  is  rowed 
on  one  side  more  strongly  than  on  the  other. 
As  a  result  the  animal  would  swim  in  circles, 
turning  continually  toward  the  aboral  side,  but 
for  the  fact  that  it  rotates  on  its  long  axis. 
Through  the  rotation  the  forward  movement  and 
the  swerving  to  one  side  are  combined  to  pro- 
duce a  spiral  course  (Fig.  33).  The  swerving 
when  the  oral  side  is  to  the  left  is  to  the  right; 
when  the  oral  side  is  above,  the  body  swerves 
downward ;  when  the  oral  side  is  to  the  right  the 
body  swerves  to  the  left,  etc.  Hence  the  swerv- 
ing in  any  given  direction  is  compensated  by  an 
equal  swerving  in  the  opposite  direction ;  the  re- 
sultant is  a  spiral  path  having  a  straight  axis. 


Fig.  33.  —  Spiral  path 
of  Paramecium.  The  fig- 
ures 1,  2,  3,  4,  etc.,  show  the 
successive  positions  occu- 
pied. The  dotted  areas 
with  small  arrows  show  the 
currents   of    water    drawn    The  spiral   swimming  is  evidently  the  resultant  of   three 

from  in  front.  factors,  —  the  forward  movement,  the  rotation  on  the  long 


The  spiral  course  plays  so  important  a  part  in  the  be- 
havior of  Paramecium  that  we  must  analyze  it  farther. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


45 


axis,  and  the  swerving  toward  the  aboral  side.  Each  of  these  factors  is  due  to  a 
certain  peculiarity  in  the  stroke  of  the  cilia.  The  first  results  from  the  fact  that  the 
cilia  strike  chiefly  backward.  The  second  is  due  to  the  fact  that  the  cilia  strike,  not 
directly  backward,  but  obliquely  to  the  right,  causing  the  animal  to  roll  over  to  the 
left.  The  third  factor  —  the  swerving  toward  the  aboral  side  —  is  due  largely  to  the 
greater  power  of  the  stroke  of  the  oral  cilia,  and  the  fact  that  they  strike  more  nearly 
directly  backward.  It  seems  partly  due  however  to  a  peculiarity  in  the  stroke  of  the 
body  cilia,  by  which  on  the  whole  they  strike  more  strongly  toward  the  oral  groove 
than  away  from  it,  thus  driving  the  body  in  the  opposite  direction. 

Each  of  these  factors  may  vary  in  effectiveness,  and  the  result  is  a  change  in  the 
movements.  The  forward  course  may  cease  completely,  or  be  transformed  into  a 
backward  course,  while  the  rotation  and  the  swerving  continue.  Or  the  rotation 
may  become  slower,  while  the 

swerving  to  the  aboral  side  a "  a " 

continues  or  increases;  then 
the  spiral  becomes  much 
wider.  This  result  is  brought 
about  by  a  change  in  the 
direction  of  the  beating  of  the 
cilia  to  the  left  of  the  oral 
groove;  they  beat  now  to  the 
left  (toward  the  oral  groove) 
instead  of  to  the  right  (Fig. 
34).  The  result  of  this  is,  as 
the  figure  shows,  to  oppose 
the  rotation  to  the  left,  but 
to  increase  the  swerving 
toward  the  aboral  side.  The 
width  of  the  spiral,  or  the  final 


Fig.  34.  —  Diagrams  of  transverse  sections  of  Parame- 
cium, viewed  from  the  posterior  end,  showing  the  change 
in  the  beat  of  the  cilia  of  the  left  side.  a,  Stroke  of  the 
cilia  in  the  usual  forward  movement.  All  the  cilia  strike 
toward  the  right  side  (r),  rotating  the  organism  to  the  left 
(I),  as  shown  by  the  arrows.  b,  Stroke  of  the  cilia  after 
stimulation.  The  cilia  of  the  left  side  strike  to  the  left, 
opposing  the  lateral  effect  of  the  cilia  of  the  right  side. 
This  causes  the  animal  to  cease  revolving,  and  to  swerve 
toward  the  aboral  side  (ab).  0,  Oral  groove, 
complete  cessation  of  the  rota- 
tion on  the  long  axis  which  sometimes  occurs,  depends  on  the  number  and  effective- 
ness of  these  cilia  of  the  left  side  that  beat  toward  the  oral  groove  instead  of  away 
from  it.  A  large  part  of  the  behavior  of  Paramecium  depends,  as  we  shall  see,  on 
the  variations  in  the  three  factors  which  produce  the  spiral  course. 


3- 


Adaptiveness  of  the  Movements 


How  does  Paramecium  meet  the  conditions  of  the  environment  ? 
Under  the  answer  to  this  question  must  be  included  certain  aspects  of 
the  spiral  movement,  described  in  the  foregoing  paragraphs.  The 
problem  solved  by  the  spiral  path  is  as  follows :  How  is  an  unsym- 
metrical  organism,  without  eyes  or  other  sense  organs  that  may  guide  it 
by  the  position  of  objects  at  a  distance,  to  maintain  a  definite  course 
through  the  trackless  water,  where  it  may  vary  from  the  path  to  the  right 
or  to  the  left,  or  up  or  down,  or  in  any  intermediate  direction?  It  is 
well  known  that  man  does  not  succeed  in  maintaining  a  course  under 


46  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

similar  but  simpler  conditions.  On  the  trackless  snow-covered  prairie 
the  traveller  wanders  in  circles,  try  hard  as  he  may  to  maintain  a  straight 
course,  —  though  it  is  possible  to  err  only  to  the  right  or  left,  not  up  or 
down,  as  in  the  water.  Paramecium  meets  this  difficulty  most  effec- 
tively by  revolution  on  the  axis  of  progression,  so  that  the  wandering 
from  the  course  in  any  given  direction  is  exactly  compensated  by  an 
equal  wandering  in  the  opposite  direction.  Rotation  on  the  long  axis 
is  a  device  which  we  find  very  generally  among  the  smaller  water  or- 
ganisms for  enabling  an  unsymmetrical  animal  to  follow  a  straight 
course.  The  device  is  marvellously  effective,  since  it  compensates  with 
absolute  precision  for  any  tendency  or  combination  of  tendencies  to 
deviate  from  a  straight  course  in  any  direction  whatsoever. 

The  normal  movements  of  Paramecium  are  adaptive  in  another 
respect.  The  same  movements  of  the  cilia  which  carry  the  animal 
through  the  water  also  bring  it  its  food.  The  oral  cilia  cause  a  current 
of  water  to  flow  rapidly  along  the  oral  groove  (Fig.  33).  In  the  water 
are  the  bacteria  upon  which  Paramecium  feeds ;  they  are  carried  by 
this  current  directly  to  the  mouth.  In  the  gullet  is  a  vibrating  membrane 
which  carries  particles  inward;  the  bacteria  which  reach  the  mouth 
are  thus  carried  through  the  gullet  to  the  endosarc,  where  they  form 
food  vacuoles  and  are  digested. 

Not  only  food,  but  also  other  substances,  may  be  brought  to  Para- 
mecium by  the  currents  due  to  the  movements  of  the  cilia.     It  is  im- 
portant for  understand- 
•V ;":'•'.;;•.,  ing  the  behavior  of  this 

;£&•&$&       animal    to    realize    that 
••:^:v^.    not    only   does    it    move 
J?  ."'^   forward  to  meet  the  en- 

£•&&$&  vironment,  but  the  en- 
';..  :;'••;  '.'•': '....  ''''■}&&''$  vironment,  so  far  as  that 
fc;.'  .       -•' V.-'':      is  possible,  also  streams 

.     .    -  ..'•.  £$0        backward     to    meet    it. 

"  ,   '  .''  If   there   is    a    chemical 

'&&0&"  diffusing  in  the  water  in 

Fig.  35.  —  Paramecium  approaching  a  region  contain-  font  Ot  It,  OT  II  tne  water 
ing  India  ink  (shown  by  the  dots).  The  India  ink  is  drawn  {§  warmer  Or  Colder,  OF 
out  to  the  anterior  end  and  oral  groove  of  the  animal.  ..„  .  ,  i 

differs  in  any  other  way, 
a  sample  of  this  differentiated  region  is  pulled  backward  in  the  form 
of  a  cone,  and  as  a  result  of  the  stronger  beating  of  the  oral  cilia, 
passes  as  a  stream  down  the  oral  groove  to  the  mouth  (Fig.  33).  This 
may  best  be  seen  by  bringing  near  the  anterior  end  of  a  resting  Parame- 
cium, by  means  of  a  capillary  pipette,  some  colored  solution,  such  as 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  47 

methyline  blue,  or  by  using  in  the  same  way  water  containing  India 
ink.  Or  if  a  cloud  of  India  ink,  with  a  definite  boundary,  is  produced 
in  the  water  containing  swimming  Paramecia,  a  cone  of  the  ink  is  seen 
to  move  out  to  meet  the  advancing  animals  (Fig.  35).  Thus  Parame- 
cium is  continually  receiving  "  samples "  of  the  water  in  front  of  it. 
Since  in  its  spiral  course  the  organism  is  successively  pointed  in  many 
different  directions,  the  samples  of  water  it  receives  likewise  come  suc- 
cessively from  many  directions  (Fig.  33).  Thus  the  animal  is  given 
opportunity  to  "try"  the  various  different  conditions  supplied  by  the 
neighboring  environment.  Paramecium  does  not  passively  wait  for 
the  environment  to  act  upon  it,  as  Amoeba  may  be  said,  in  com- 
parison, to  do.  On  the  contrary,  it  actively  intervenes,  determining 
for  itself  what  portion  of  the  environment  shall  act  upon  it,  and  in 
what  part  of  its  body  it  shall  be  primarily  affected  by  the  varying  con- 
ditions of  the  surrounding  water.  By  thus  receiving  samples  of  the 
environment  for  a  certain  distance  in  advance,  it  is  enabled  to  react 
with  reference  to  any  new  condition  which  it  is  approaching,  before  it 
has  actually  entered  these  conditions. 

4.   Reactions  to   Stimuli 

Let  us  suppose  that  as  Paramecium  swims  forward  in  the  way  just 
described,  it  receives  from  in  front  a  sample  that  acts  as  a  stimulus, — 
that  is  perhaps  injurious.  The  ciliary  current  brings  to  its  anterior 
end  water  that  is  hotter  or  colder  than  usual,  or  that  contains  some 
strong  chemical  in  solution,  or  holds  large  solid  bodies  in  suspension,  or 
the  infusorian  strikes  with  its  anterior  end  against  a  solid  object.  What 
is  to  be  done? 

Paramecium  has  a  simple  reaction  method  for  meeting  all  such 
conditions.  It  first  swims  backward,  at  the  same  time  necessarily  / 
reversing  the  ciliary  current.  It  thus  gets  rid  of  the  stimulating  agent, 
—  itself  backing  out  of  the  region  where  this  agent  is  found,  while  it 
drives  away  the  stimulus  in  its  reversed  ciliary  current.  It  then  turns 
to  one  side  and  swims  forward  in  a  new  direction.  The  reaction  is 
illustrated  in  Fig.  36.  The  animal  may  thus  avoid  the  stimulating 
agent.  If,  however,  the  new  path  leads  again  toward  the  region  from 
which  the  stimulus  comes,  the  animal  reacts  in  the  same  way  as  at  first, 
till  it  finally  becomes  directed  elsewhere.  We  may  for  convenience 
call  this  reaction,  by  which  the  animal  avoids  all  sorts  of  agents,  the 


"avoiding  reaction." 


In  the  foregoing  paragraph  we  have  given  only  a  general  outline  of 
the  behavior.     The  avoiding  reaction  has  certain  additional  features, 


4§ 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


which  add  greatly  to  its  effectiveness.     After  getting  rid  of  the  stimulus 
by  swimming  backward  a  distance  there  must  be  some  way  of  deter- 


Fig.  36.  —  Diagram  of  the  avoiding  reaction  of  Paramecium.  A  is  a  solid  object  or  other 
source  of  stimulation.  1-6,  successive  positions  occupied  by  the  animal.  (The  rotation  on  the 
long  axis  is  not  shown.) 

mining  the  new  direction  in  which  the  animal  is  to  swim  forward.  It 
is  evident  that  some  method  of  testing  the  conditions  in  various  different 
directions  in  advance  would  be  the  most  effective  way  of  accomplishing 
this.  The  infusorian  now  moves  in  precisely  such  a  way  as  to  make 
such  tests.  It  will  be  recalled  that  in  its  usual  course  the  animal  is 
revolving  on  the  long  axis  and  swerving  a  little  toward  the  aboral  side 
(Fig.  33),  so  that  it  swims  in  a  narrow  spiral.  After  swimming  back- 
ward a  certain  distance  in  response  to  stimulation,  the  revolution  on  the 
long  axis  becomes  slower,  while  the  swerving  toward  the  aboral  side  is 
increased.  As  a  result  the  anterior  end  swings  about  in  a  large  circle; 
the  animal  becomes  pointed  successively  in  many  different  directions, 
as  illustrated  in  Figs.  37  and  38.  From  each  of  these  directions  it 
receives  in  its  ciliary  vortex  a  "sample"  of  the  water  from  immediately 
in  advance,  as  the  figures  show.  As  long  as  the  samples  contain  the 
stimulating  agent,  —  the  hot  or  cold  water,  the  chemical,  or  the  like,  — 
the  animal  holds  back  and  continues  to  swing  its  anterior  end  in  a 
circle  —  "trying"  successively  many  different  directions.  When  the 
sample  from  a  certain  direction  no  longer  contains  the  stimulating  agent, 
the  animal  simply  resumes  its  forward  course  in  that  direction.  Thus 
its  path  has  been  changed,  so  that  it  does  not  enter  the  region  of  the 
chemical  or  the  hot  or  cold  water.  Mechanical  obstacles  are  avoided 
in  precisely  the  same  way,  save  that  of  course  the  ciliary  vortex  does 
not  bring  samples  of  the  stimulating  agent,  so  that  the  infusorian  is 
compelled  to  try  starting  forward  repeatedly  in  various  directions,  be- 
fore it  finds  one  in  which  it  can  pass  freely. 


THE   BEHAVIOR    OF   INFUSORIA;  PARAMECIUM 


49 


This  method  of  behaving  is  perhaps  as  effective  a  plan  for  meeting 
all  sorts  of  conditions  as  could  be  devised  for  so  simple  a  creature.  On 
getting  into  difficulties  the  animal  retraces  its  course  for  a  distance, 
then  tries  going  ahead  in  various  directions,  till  it  finds  one  in  which 
there  is  no  further  obstacle  to  its  progress.  In  this  direction  it  continues. 
Through  systematically  testing  the  surroundings,  by  swinging  the  an- 
terior end  in  a  circle,  and  through  performing  the  entire  reaction  re- 
peatedly, the  infusorian  is  bound  in  time  to  find  any  existing  egress  from 
the  difficulties,  even  though  it  be  but  a  narrow  and  tortuous  passageway. 

The  different  phases  of  this  avoiding  reaction  are  evidently  due  to  modifications 
of  the  three  factors  in  the  spiral  course.  The  swimming  backward  is  due  of  course 
to  a  reversal  of  the  forward  stroke  of  the  cilia.  The  turning  toward  the  aboral  side 
is  an  accentuation  of  the  swerving  that  takes  place  always;  it  is  due  to  the  fact  that 
the  cilia  at  the  left  side  of  the  body  strike  during  the  reaction  toward  the  oral  groove 
instead  of  away  from  it.  Thus  the  cilia  of  both  right  and  left  sides  now  tend  to  turn 
the  animal  toward  the  aboral  side.  The  difference  between  the  usual  condition  and 
that  found  during  the  reaction  is  illustrated  in  Fig.  34.  Finally,  the  decrease  or 
cessation  in  the  revolution  on  the  long  axis  is  due  to  the  same  factor  as  the  increase 
in  swerving  toward  the  aboral  side.  During  the  reaction  the  cilia  of  the  left  side 
oppose  the  usual  revolution  on  the  long  axis  to  the  left  (as  shown  in  Fig.  34), 
through  the  same  change  which  causes  them  to  assist  in  turning  the  body  toward  the 
aboral  side. 

The  avoiding  reaction  varies  greatly  under  different  conditions, 
though  its  characteristic  features  are  maintained  throughout.  But  its 
different  phases  vary  in  intensity  depending 
on  circumstances.  The  backward  movement 
may  be  long  continued,  or  may  last  but  a 
short  time ;  or  there  may  be  merely  a  stop- 
page or  slowing  of  the  forward  movement. 
The  swerving  toward  the  aboral  side  may  be 
only  slightly  increased,  while  the  revolution 
on  the  long  axis  becomes  a  little  slower.  In 
this  case  the  anterior  end  swings  about  in 
a  small  circle,  as  in  Fig.  37,  so  that  the  ani- 
mal is  pointed  successively  in  a  number  of 
directions  varying  only  a  little  from  the  origi- 
nal one.  With  a  stronger  stimulus  the  swerv- 
ing toward  the  aboral  side  is  more  decided, 
while  the  rotation  on  the  long  axis  is  slower; 
then  the  anterior  end  swings  about  a  larger 
circle,  as  in  Fig.  38.  The  Paramecium  thus 
becomes  pointed  successively  in  many  directions  differing  much  from 
the    original  one.     Finally,   the  rotation  on  the  long  axis  may  com- 


it->x 


Fig  .  37.  —  Paramecium 
swinging  its  anterior  end  about  in 
a  small  circle,  in  a  weak  avoiding 
reaction.  1,  2,  3,  4,  successive 
positions  occupied. 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


pletely  cease,  while   the  swerving   toward  the    aboral    side   is  farther 
increased ;    then  the  Paramecium  swings  its  anterior  end  about  a  circle 

with  its  posterior 

i 


si 


Fig.  38.  —  More  pronounced  avoiding  reaction.     The  anterior  end 
swings  about  a  larger  circle.     1-5,  successive  positions  occupied. 


end  near  the cen- 
tre (Fig.  39).  In 
this  case  the 
animal  may  turn 
directly  away 
from  the  stimu- 
lating agent. 

Such  varia- 
tions are  seen 
when  the  infu- 
soria are  sub- 
jected to  stimuli 
of  different  in- 
tensities.    If  the 

animals  come  in  contact  with  any  strong  chemical,  or  with  water  that  is 

very  hot,  they  respond  first  by  swimming  a  long  way  backward,  thus 

removing  themselves  as  far  as 

possible    from    the    source    of 

stimulation.      Then  they  turn 

directly    toward     the     aboral 

side,  —  the    rotation    on    the 

long  axis    completely  ceasing, 

as  in  Fig.  39.     In  this  way  the 

animal  may  turn  directly  away 

from  the  drop  and  retrace  its 

course.  But  often  the  reac- 
tion is  so  violent  that  the  an- 
terior end  swings  about  in  two 

or  three  complete  circles  before 

the     animal     starts     forward 

again.      Then   the   new  path 

may  lead  it  again  toward  the 

drop,    when    the    reaction    is 

repeated. 

In    marked  contrast   with 

this  violent  reaction  is  the  behavior  when  the  stimulus  is  very  weak. 

A  weak  stimulus  is  produced  for  example  by  -^  per  cent  to  -^  per 

cent  sodium  chloride,  or  by  water  only  three  or  four  degrees  above  the 

normal   temperature.     The    Paramecium  whose  oral   cilia   bring   it  a 


Fig.  30. — Avoiding  reaction  when  revolution  on 
the  long  axis  ceases  completely.  The  anterior  end 
swings  about  a  circle  of  which  the  body  forms  one  of 
the  radii. 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  51 

sample  of  such  water  merely  stops,  or  progresses  more  slowly,  and 
begins  to  swing  its  anterior  end  about  in  a  circle,  as  in  Fig.  37,  thus 
"trying"  a  number  of  different  directions.  As  long  as  the  oral  cilia 
continue  to  bring  it  the  weak  salt  solution  or  the  warmed  water,  the 
animal  holds  back,  and  continues  to  swing  its  anterior  end  about  in  a 
circle.  When  the  anterior  end  is  finally  pointed  in  a  direction  from 
which  no  more  of  the  stimulating  agent  comes,  the  Paramecium 
swims  forward.  The  reaction  in  this  case  is  a  very  precise  and  delicate 
one;  in  a  cursory  view  the  animal  seems  to  turn  directly  away  from 
the  region  of  the  stimulus,  —  the  revolution  on  the  long  axis  and  swing- 
ing of  the  anterior  end  in  a  circle  being  easily  overlooked. 

Between  this  delicate  reaction  and  the  violent  one  first  described 
there  exists  every  intermediate  gradation,  depending  on  the  intensity  of 
the  stimulation. 

Paramecia  react  to  most  of  the  different  classes  of  stimuli  which  act 
upon  them,  in  the  way  just  described.  Mechanical  stimuli,  such  as 
solid  obstacles,  or  disturbances  in  the  water;  chemicals  of  all  sorts; 
heat  and  cold  ;  light  that  is  sufficiently  powerful  to  be  injurious;  electric 
shocks,  and  certain  disturbances  induced  by  gravity  and  by  centrifugal 
force,  all  cause  the  animal  to  respond  by  the  avoiding  reaction,  so  that 
it  escapes  if  possible  from  the  region  or  condition  that  acts  as  a  stimulus. 
Certain  peculiarities  and  special  features  in  the  action  of  the  different 
classes  of  stimuli  will  be  taken  up  separately  in  the  following  chapters. 

Stimulating  agents  produce  the  same  reaction  when  they  act  on  the 
entire  surface  of  the  body  as  they  do  when  they  reach  only  the  anterior 
end  or  oral  groove.  This  is  shown  by  dropping  the  animals  directly 
into  a  |r  per  cent  solution  of  sodium  chloride,  or  into  corresponding 
solutions  of  other  chemicals ;  or  into  hot  or  cold  water.  They  at  once 
give  the  avoiding  reaction ;  they  swim  backward,  turn  toward  the  aboral 
side,  then  swim  forward,  and  this  reaction  may  be  repeated  many  times. 
If  the  stimulating  agent  is  not  so  powerful  as  to  be  directly  destructive, 
the  reaction  ceases  after  a  time,  and  the  Paramecia  swim  about  within 
the  solution  as  they  did  before  in  water. 

This  experiment  shows  clearly  that  the  cause  of  the  avoiding  reaction 
does  not  lie  in  the  difference  in  the  intensity  of  the  chemical  on  the  two 
sides  or  two  ends  of  the  animal,  as  is  sometimes  held.  For  as  we  have 
just  seen,  the  animal  reacts  in  the  same  way  when  the  entire  surface  of 
the  body  is  subjected  equally  to  the  action  of  the  chemical  or  the  changed 
temperature.  It  is  clear  that  the  cause  of  the  reaction  is  the  changel 
from  one  solution  or  temperature  to  another.  This  is  evident  further' 
from  the  fact  that  the  animal  reacts  as  a  rule  when  the  change  occurs, 
but  ceases  to  react  after  the  change  is  completed.     To  constant  con- 


52  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

ditions  Paramecium  soon  becomes  acclimatized ;  it  is  change  that 
causes  reaction. 

To  this  general  statement  there  are  certain  exceptions.  If  we  place 
the  infusoria  in  conditions  of  such  intense  action  that  they  are  quickly 
destructive,  —  for  example,  in  2  per  cent  potassium  bichromate,  or 
in  water  heated  to  38  degrees  C, — the  animals  continue  to  react  till  they 
die.  For  two  or  three  minutes  they  rapidly  alternate  swimming  back- 
ward with  turning  toward  the  aboral  side  and  swimming  forward, 
till  death  puts  an  end  to  their  activity.  Thus  very  injurious  conditions 
may  produce  reaction  independently  of  change.  But  as  a  general  rule, 
it  is  some  change  in  the  conditions  that  causes  the  animal  to  change  its 
behavior.  The  animal,  having  been  subjected  to  certain  conditions, 
becomes  now  subjected  to  others,  and  it  is  the  transition  from  one  state 
to  another  that  is  the  cause  of  reaction.  This  is  a  fact  of  fundamental 
significance  for  understanding  the  behavior  of  lower  organisms. 

But  it  is  not  mere  change,  taken  by  itself,  that  causes  reaction,  but 
change  in  a  certain  direction.  This  is  shown  by  observation  of  the 
behavior  of  the  individuals  as  they  pass  from  one  set  of  conditions  to 
another.  If  we  place  Paramecia  on  a  slide  in  ordinary  water,  then  in- 
troduce into  the  preparation,  by  means  of  a  capillary  pipette,  a  drop  of 
^  per  cent  sodium  chloride,  as  shown  in  Fig.  40,  we  find  that  the 
animals  react  at  the  change  from  the  water  to  the  salt  solution,  so  that 
they  do  not  enter  the  latter.  If,  on  the  other  hand,  the  animals  are  first 
mixed  with  ^  per  cent  salt  solution,  and  a  drop  of  water  is  introduced 
into  the  preparation  (as  in  Fig.  40),  they  do  not  react  at  passing  from  the 
salt  solution  to  the  water.  In  the  same  way,  Paramecia  at  a  temperature 
of  30  degrees  react  at  passing  to  a  higher  temperature,  but  not  at  passing 
to  a  lower  temperature.  Paramecia  at  20  degrees,  on  the  other  hand, 
react  at  passing  to  a  lower  temperature,  not  at  passing  to  a  higher.  To 
these  relations  we  shall  return. 

A  relation  which  is  worthy  of  special  emphasis  is  the  following :  The 
direction  toward  which  the  animal  turns  in  the  avoiding  reaction  does 
not  depend  on  the  side  of  the  animal  that  is  stimulated,  but  is  deter- 
mined by  internal  relations.  The  animal  always  turns  toward  the  aboral 
side.  It  is  true  that  with  chemical  stimuli  the  stimulation  usually 
occurs  on  the  oral  side,  so  that  the  animal  turns  away  from  the  side 
stimulated.  But,  as  we  have  just  seen,  it  turns  in  the  same  way  when 
all  parts  of  the  body  are  equally  affected  by  the  stimulating  agent. 
Furthermore,  it  is  possible  to  apply  mechanical  stimuli  to  various  parts 
of  the  body,  and  observe  the  resulting  reaction.  If  with  the  tip  of  a  fine 
glass  point  we  touch  the  oral  side  of  Paramecium,  the  infusorian  turns 
directly  away  from  the  point  touched.     But  if  we  touch  the  aboral  side, 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


53 


the  Paramecium  turns  in  the  same  manner  as  before,  —  toward  the 
aboral  side,  and  hence  toward  the  point  touched.  This  experiment  is 
more  easily  performed,  and  the  results  are  more  striking,  with  certain 
of  the  Hypotricha,1  because  these  animals  do  not  continually  revolve  on 
the  long  axis,  as  Paramecium  does. 

The  general  effect  of  the  avoiding  reaction  is  to  cause  the  animals 
to  avoid  and  escape  from  the  region  in  which  the  stimulus  is  acting. 
This  may  be  illustrated  for  the  different  classes  of  stimuli  in  the  follow- 
ing ways. 

The  effects  of  this  reaction  to  chemicals  may  best  be  seen  by  intro- 
ducing a  little  ^  per  cent  solution  of  sodium  chloride  into  the  water 
containing  the  ani- 
mals. For  this  pur- 
pose water  with  many 
Paramecia  is  placed 
on  a  slide  and  covered 
with  a  long  cover- 
glass  supported  near 
its  end  by  glass  rods. 
A  medicine  dropper 
is  drawn  to  a  long, 
slender  point,  and  with 
this  a  drop  of  the  salt 
solution  is  introduced 

beneath  the  cover-glass,  as  illustrated  in  Fig.  40.  The  Paramecia  are 
swimming  about  in   all  directions,  but   as   soon   as   they  come  to  the 

region  of  the  salt  solution,  the 
avoiding  reaction  is  given  in  the 
way  already  described,  and 
the  animals  swim  elsewhere. 
Thus  the  drop  of  salt  solution 
remains  empty  (Fig.  41). 

Practically  all  strong  chemicals 

Fig.  41.-  Slide  of  Paramecia  four  minutes    ™d"^    the    avoiding    reaction,    SO 

after  the  introduction  of  a  drop  of  \  per  cent   that  Paramecia  do  not  enter  them. 

NaCl.     The  drop  remains  empty.  Thig    ^    bgen    ghown    ^    many 

alkalies,  neutral  salts,  and  organic  substances,  and  for  strong  acids. 
In  the  case  of  acids  the  reaction  differs  in  certain  respects  from  the 
behavior  under  the  influence  of  other  chemicals ;  this  will  be  brought 
out  later. 

The  reaction  to  heat  or  cold  may  easily  be  shown  by  placing  a  drop 

iSee  Chapter  VII. 


Fig.  40.  —  Method  of  introducing  a  chemical  into  a  slide 
of  infusoria. 


54  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

of  hot  or  cold  water  on  the  cover-glass  of  a  slide  of  Paramecia,  or  by 
touching  the  cover-glass  with  a  hot  wire,  or  a  piece  of  ice.  The  animals 
respond  by  the  avoiding  reaction,  just  as  when  stimulated  by  a  chemical, 
so  that  the  hot  or  cold  region  remains  vacant.  The  intensity  of  the  re- 
action depends  on  the  temperature,  and  very  hot  water  causes  a  much 
more  decided  reaction  than  very  cold  water. 

The  avoiding  reaction  is  seen  under  mechanical  stimulation  when  a 
specimen  in  swimming  comes  against  an  obstacle.  It  may  also  be  shown 
by  touching  the  anterior  end  of  the  animal  with  a  fine  glass  point.  A 
slight  disturbance  in  the  water  may  be  induced  by  injecting  a  fine 
stream  of  water  against  the  animal  with  a  pipette  drawn  to  a  capillary 
point ;  the  animal  then  responds  by  the  avoiding  reaction,  thus  swimming 
elsewhere. 

Special  features  in  the  reactions  to  various  different  classes  of  stimuli 
will  be  dealt  with  in  the  next  chapter. 

5.   "  Positive  Reactions  " 

The  reactions  thus  far  described  have  the  effect  of  removing  the 
animal  from  the  source  of  stimulation ;  they  might  therefore  be  charac- 
terized as  negative.  But  Paramecia  are  known  also  to  collect  in  certain 
regions,  giving  rise  to  what  are  commonly  known  as  positive  reactions. 
How  are  these  brought  about  ? 

A  simple  experiment  throws  much  light  on  the  cause  of  such  col- 
lections. Under  usual  conditions  the  animals  avoid  a  -^o  Per  cent  solu- 
tion of  NaCl,  so  that  when  a  drop  of  this  is  introduced  into  a  slide  of 
Paramecia,  they  leave  it  empty.  But  if  we  mix  the  animals  with  ^  per 
cent  NaCl,  then  introduce  into  a  slide  of  this  mixture  a  drop  of 
Yjj  per  cent  NaCl,  in  the  way  shown  in  Fig.  40,  we  find  that  the  Para- 
mecia quickly  collect  in  this  drop,  though  under  ordinary  circumstances 
they  avoid  it.  Very  soon  the  drop  of  -^0  Per  cent  NaCl  is  swarming  with 
the  infusoria,  as  in  Fig.  43,  while  very  few  remain  in  other  parts 
of  the  preparation.  The  phenomena  are  identical  with  what  has  often 
been  called  positive  chemotaxis. 

Careful  observation  of  the  movements  of  the  individuals  shows, 
as  might  be  expected,  that  the  Paramecia  collect  in  the  ytj-  Per  cent  NaCl 
merely  because  they  avoid  the  stronger  solution  more  decidedly.  Pas- 
sage from  the  -^  per  cent  solution  to  the  -|-  per  cent  solution  causes  the 
avoiding  reaction,  while  passage  in  the  reverse  direction  does  not.  The 
details  of  the  behavior  are  as  follows  :  The  Paramecia  in  the  -|-  per  cent 
NaCl  are  swimming  rapidly  in  all  directions,  so  that  many  of  them  are 
carried  toward  the  drop.     On  reaching  its  boundary  they  do  not  react 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  55 

in  any  way,  but  swim  directly  into  it.  They  continue  across  till  they 
reach  the  farther  boundary,  where  they  come  in  contact  again  with  the 
\  per  cent  solution.  Here  the  reaction  occurs.  The  animals  give 
the  avoiding  reaction,  swimming  backward,  turning  toward  the  aboral 
side,  and  starting  forward  again,  etc.  They  of  course  soon  come  in 
contact  again  with  the  outlying  -|-  per  cent  NaCl,  whereupon  they  react 
as  before,  and  this  continues,  so  that  they  do  not  leave  the  drop  of  jq  per 
cent  NaCl.  The  path  of  a  single  Paramecium  in  such  a  drop  is  like 
that  shown  in  Fig.  44.  Since  all  the  infusoria  that  enter  the  drop  of 
Yq  per  cent  NaCl  remain,  it  soon  swarms  with  them. 

In  place  of  NaCl,  we  may  use  pairs  of  solutions  of  other  chemicals, 
one  stronger  than  the  other,  —  taking  pains  of  course  not  to  employ 
concentrations  that  are  decidedly  injurious.  With  any  of  the  ordinary 
inorganic  salts  or  alkalies  the  animals  collect  in  the  weaker  solution, 
through  the  fact  that  they  avoid  the  stronger  one  in  the  way  described 
above.  The  same  concentration  of  a  given  chemical  may  play  opposite 
roles  in  successive  experiments,  depending  on  whether  it  is  associated 
with  a  weaker  or  a  stronger  solution.  In  the  former  case  the  Paramecia 
avoid  it ;  in  the  latter  they  gather  within  it.  If  the  weaker  solution  sur- 
rounds a  drop  of  the  stronger,  the  latter  is  left  empty,  and  the  Para- 
mecia remain  scattered  through  the  preparation,  as  in  Fig.  41.  If 
the  stronger  solution  surrounds  the  weaker,  the  latter  becomes  filled 
with  the  Paramecia,  as  in  Fig.  43,  while  the  former  is  left  nearly 
empty.  Thus  with  the  same  pair  of  substances  we  get  either  a  dense 
aggregation  (or  what  is  often  called  positive  chemotaxis),  or  a  certain 
area  left  vacant  ("negative  chemotaxis"),  depending  on  the  relation 
of  the  two  fluids  to  each  other. 

If  we  use  pure  water  in  place  of  the  weaker  solution,  we  get  the  same 
result ;  the  Paramecia  collect  in  the  drop  of  water.  This  is  easily  shown 
by  introducing  a  drop  of  water  into  a  preparation  of  Paramecia  that  have 
been  mixed  with  ^  per  cent  NaCl ;  the  water  soon  swarms  with  the  in- 
fusoria. The  culture  water  in  which  Paramecia  live  usually  contains 
various  salts,  and  is  often  alkaline  in  reaction.  If  a  drop  of  distilled 
water  is  added  (as  in  Fig.  40)  to  a  preparation  of  infusoria  in  such 
culture  water,  the  animals  gather  in  the  distilled  water. 

The  same  results  may  be  obtained  with  water  of  differing  tempera- 
tures. This  is  done  by  surrounding  an  area  of  water  at  the  normal 
temperature  with  water  at  a  temperature  considerably  higher  or  lower. 
The  Paramecia  may  be  placed  on  a  slide  in  the  usual  way,  with  a  cover- 
glass  supported  by  glass  rods.  This  slide  is  then  placed  on  a  bottle 
or  other  vessel  containing  water  heated  to  forty-five  or  fifty  degrees. 
As  soon  as  the  Paramecia  begin  to  move  about  more  rapidly  in  conse- 


56 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


-  a 


quence  of  the  heat,  a  drop  of  cold  water  is  placed  on  the  upper  surface 
of  the  cover-glass.     At  once  a  dense  collection  of  Paramecia  is  formed 

beneath  it  (Fig.  42).  Observation  of 
the  movements  of  the  individuals 
shows  that  this  collection  is  formed  in 
the  same  way  as  the  collections  pro- 
duced in  chemicals  (Figs.  43,  44, 
etc.).  The  Paramecia  at  a  distance 
fig.  42.  -  a  slide  of  Paramecia  is    from   the  cooled   region   do   not   turn 

heated  to  40  or  45  degrees,  then  a  drop  of     ancJ  SWim  directly  toward  it.       But    the 
cold  water  (represented  by  the  outline  a)  .  .  .... 

is  placed  on  the  upper  surface  of  the    Paramecia    are    swimming    rapidly  in 
cover-glass.    The  animals  collect  beneath    q]\  directions,  and  manv    enter   every 

this  drop,  as  shown  in  the  figure.  .  .  .  .         '1,1         1 

instant  the  region  beneath  the  drop. 
They  do  not  react  on  entering,  but  on  reaching  the  opposite  side,  where 
they  would  pass  out  again  into  the  heated  water,  they  give  the  avoid- 
ing reaction.  This  is  repeated  every  time  they  come  to  the  other 
boundary  of  the  drop,  so  that 
the  path  of  an  individual  within 


the  cooled  region  is  similar  to  that 
shown   in    Fig 


* 

- 

• 

- 

- 

l|J2f\ 

• 

'/ 

- 

\ 

• 

Fig.   43.  —  Collection    of    Paramecia    in   a 
drop  of  ^5  per  cent  acetic  acid. 


44.  Every  Para- 
mecium that  enters  the  cooled 
region  therefore  remains,  and 
soon  a  dense  swarm  is  formed. 

A  collection  may  be  formed  in 
the  same  way  by  resting  the  slide 
of  Paramecia  on  a  piece  of  ice  and 
placing  a  drop  of  warmed  water  on  the  upper  surface ;  the  Paramecia 
now  collect  in  the  warmed  region.  But  the  collection  is  never  so  pro- 
nounced as  in  the  experiment  last  described,  because  the  Paramecia 
when  cooled  move  less  rapidly. 

Thus  the  Paramecia  collect  in  certain  regions  because  they  give 
the  avoiding  reaction  when  passing  from  certain  conditions  to  others, 
while  when  passing  in  the  reverse  direction  they  do  not.  Paramecia 
at  the  normal  temperature  give  the  reaction  at  passing  both  to  hotter 
and  to  colder  water;  they  therefore  tend  to  gather  in  water  at  the  usual 
temperature.  This  temperature  at  which  they  gather  may  be  spoken 
of  as  the  optimum.  Passage  away  from  the  optimum  induces  the 
avoiding  reaction ;   passage  toward  the  optimum  does  not. 

In  the  case  of  the  chemicals  thus  far  considered,  the  animals  give 
the  reaction  at  passing  from  the  weaker  to  the  stronger  solution,  not  at 
passing  in  the  opposite  direction,  so  that  they  collect  in  the  weaker  solu- 
tion.    The  optimum  for  these  substances  is  thus  zero,  and  this  natu- 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  57 

rally  results  in  the  tendency  of  the  animals  to  collect  in  distilled  water. 
But  there  are  certain  chemicals  of  which  the  optimum  is  a  certain  posi- 
tive concentration,  so  that  Paramecia  give 
the  avoiding  reaction  at  passing  to  weaker 
solutions  or  to  water  containing  none  of 
the  substance  in  question.  This  is  the 
case  with  acids  and  with  oxygen.  If  a 
drop  of  very  weak  acid  is  introduced  into 
a  slide  of  Paramecia  (Fig.  43)  that  are  in 
ordinary  water,  the  animals  quickly  gather 
in  the  drop.  This  may  be  shown  by  the 
use  of  about  y^-g  to  Jjy  per  cent  of  the  ordi- 
nary laboratory  solutions  of  hydrochloric 
or  sulphuric  acid,  or  of  -^  to  ^5  per  cent  Fig.  44.  —  Path  followed  by  a 
acetic   acid.     In   a  short  time^the  drop  is    sin*=le  Paramecium  in  a  drop  of 

1  acid. 

swarming  with  Paramecia.1 

Observation  shows  that  the  method  of  collecting  in  the  acid  is  the 
same  as  in  the  cases  before  described.  The  rapid  movements  of  the 
animals  in  all  directions  are  what  carry  them  into  the  drop.  They  do 
not  react  in  any  way  at  the  moment  of  entering  it,  but  swim  across. 
At  the  point  where  they  would  pass  out  into  the  surrounding  water  they 
respond  by  the  avoiding  reaction ;  hence  they  return  to  the  acid.  This 
is  repeated  each  time  that  they  come  to  the  boundary.  Hence  all  that 
enter  the  acid  remain  till  it  is  crowded.  The  path  of  a  single  Parame- 
cium within  a  drop  of  acid  is  shown  in  Fig.  44. 

In  the  formation  of  all  these  collections  the  natural  roving  move- 
ments play  an  essential  part.  These  movements  cause  any  given  speci- 
men in  the  course  of  a  short  time  to  cross  almost  any  given  area  in  the 
preparation,  and  hence  bring  the  animals  to  the  introduced  drop.  The 
animals  do  not  turn  and  swim  in  radial  lines  toward  the  drop  of  acid. 
If  a  ring  is  marked  on  the  upper  surface  of  the  cover-glass,  as  many 
Paramecia  will  be  found  to  pass  beneath  this  ring  before  a  drop  of  acid 
is  placed  beneath  it  as  after.  But  in  the  latter  case  all  that  pass  beneath 
the  ring  remain,  and  the  collection  results.  If  we  wait,  before  introduc- 
ing the  acid,  till  all  have  become  nearly  quiet,  no  collection  is  produced. 

We  may  sum  up  the  usual  behavior  of  Paramecium  under  the  vari- 
ous stimuli  of  the  environment  in  the  following  way.  The  natural 
condition  of  the  animal  is  movement.  In  constant  external  conditions 
(unless  destructive)  the  movements  are  not  changed,  —  that  is,  there 

1  In  all  these  experiments  it  is  assumed,  of  course,  that  the  preparation  contains  the 
infusoria  in  very  large  numbers.  With  scattered  specimens  only,  the  results  are  slow  and 
not  striking. 


58  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

is  no  reaction,  —  even  though  these  conditions  do  not  represent  the 
optimum.  But  as  its  movements  carry  the  animal  from  one  region  to 
another,  the  environmental  conditions  affecting  it  are  of  course  changed, 
and  some  of  these  changes  in  condition  act  as  stimuli,  causing  the  ani- 
mal to  change  its  movements.  If  the  environmental  change  leads 
toward  the  optimum,  there  is  no  reaction,  but  the  existing  behavior  is 
continued.  To  a  change  leading  away  from  the  optimum  (in  either  a 
plus  or  minus  direction),  Paramecium  responds  by  the  "avoiding  reac- 
tion." This  consists  essentially  in  a  return  to  a  previous  position, 
through  a  backward  movement,  then  in  "trying"  different  directions  of 
movement  till  one  is  found  which  leads  toward  the  optimum.  Ex- 
pressed in  a  purely  objective  way,  the  animal  performs  movements 
which  subject  it  successively  to  many  different  environmental  condi- 
tions. As  soon  as  one  of  the  conditions  thus  reached  is  of  such  a  char- 
acter as  to  remove  the  cause  of  stimulation,  the  avoiding  reaction  ceases 
and  the  infusorian  continues  in  the  condition  now  existing.  This 
method  of  reacting  causes  the  animals  to  collect  in  certain  regions  (as 
near  the  optimum  as  possible),  and  to  avoid  other  regions.  Thus  are 
produced  the  so-called  positive  and  negative  reactions.  The  behavior 
may  be  characterized  briefly  as  a  selection  from  the  environmental  con- 
ditions resulting  from  varied  movements. 

Some  details  of  the  behavior  under  the  different  classes  of  stimuli 
will  be  given  in  the  next  chapter. 

LITERATURE   III 

On  the  character  of  the  movements  and   reactions  of  Paramecium :  Jennings 
1904  h,  1899,  1 90 1. 


CHAPTER   IV 

BEHAVIOR   OF   PARAMECIUM    {Continued) 

Special  Features  of  the  Reactions  to  a  Number  of  Differ- 
ent Classes  of  Stimuli 

In  the  preceding  chapter  the  general  method  of  the  reactions  of 
Paramecium  to  most  classes  of  stimuli  has  been  described.  In  the 
present  chapter  certain  important  details  and  special  peculiarities  of 
the  behavior  under  the  different  classes  of  stimuli  will  be  described. 

i.    mechanical  stimuli 

When  Paramecium  strikes  in  its  forward  course  against  a  solid  ob- 
ject, it  responds  usually  by  the  avoiding  reaction,  as  described  in  the 
preceding  chapter.  In  such  cases  the  stimulus  affects  the  anterior  end 
of  the  animal.  But  if  mechanical  stimuli  affect  other  parts  of  the  body, 
will  this  alter  the  nature  of  the  reaction?  This  question  may  be  an- 
swered by  drawing  a  glass  rod  to  an  extremely  fine  point  and  touching 
various  parts  of  the  body  with  this  point  under  the  microscope.  The 
first  discovery  that  we  make  by  this  method  of  experimentation  is  that 
the  anterior  end  is  much  more  sensitive  than  the  remainder  of  the  body 
surface.  If  the  anterior  end  is  touched  very  lightly,  the  animal  responds 
by  a  strong  avoiding  reaction,  while  the  same  or  a  more  powerful  stimu- 
lus on  other  parts  of  the  body  produces  no  reaction  at  all.  There  is 
some  evidence  drawn  from  other  sources1  that  the  region  immediately 
about  the  mouth  is  likewise  very  sensitive. 

A  second  fact  brought  out  by  these  experiments  is  that  a  stimulus 
on  the  posterior  part  of  the  body  produces  a  different  reaction  from  a 
stimulus  in  front.  If  we  touch  the  anterior  end,  or  any  point  on  the 
anterior  portion  of  the  body  back  nearly  to  the  middle,  the  typical  avoid- 
ing reaction  is  produced.  But  if  we  touch  the  middle  or  the  posterior 
part  of  the  body  of  a  resting  specimen,  the  animal,  if  it  reacts  at  all, 
merely  moves  forward. 

1  See  Chapter  V. 
59 


6o 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


On  the  other  hand,  as  we  have  seen  in  the  preceding  chapter,  the 
direction  in  which  the  animal  turns  in  the  avoiding  reaction  does  not 
depend  on  the  side  of  the  body  stimulated.  The  animal  turns  toward 
the  aboral  side  as  well  when  that  side  is  touched,  as  when  the  oral  side 
receives  the  stimulus. 

The  reactions  which  we  have  thus  far  described  have  the  effect  of 
removing  the  animal  from  the  object  with  which  it  comes  in  contact,  so 
that  they  may  be  called  negative  reactions.  But  under 
certain  conditions,  not  very  precisely  definable,  Paramecium 
does  not  avoid  the  object  which  it  strikes  against.  On  the 
contrary  it  stops  and  remains  in  contact  with  the  object. 
This  seems  most  likely  to  happen  when  the  animal  is  swim- 
ming slowly,  so  that  it  does  not  strike  the  object  violently. 
But  this  does  not  explain  all  cases;  many  individuals  seem 
much  inclined  to  come  to  rest  against  solids,  while  others  do 
not.  Often  all  the  individuals  in  a  culture  are  thus  inclined 
to  come  to  rest,  while  in  another  culture  all  remain  free 
swimming,  and  give  the  avoiding  reaction  whenever  they 

a  single  swim- 


Fro.  45- 
—  Parame- 
cium at  rest 
against  a 
cotton  fibre, 
showing  the 
motionless 
cilia  in  con- 
tact with  the 
fibre. 


come  in  contact  with  a  solid. 


Observing 


ming  specimen,  it  is  often  seen  to  react  as  follows.  When 
it  first  strikes  against  an  object  it  responds  with  a  weak 
avoiding  reaction,  —  swimming  backward  a  short  distance, 
turning  a  little  toward  the  aboral  side,  then  swimming  for- 
ward again.  Its  path  carries  it  against  the  object  again, 
whereupon  it  stops  and  comes  to  rest  against  the  surface. 

The  objects  against  which  Paramecium  strikes  under  normal  con- 
ditions are  usually  pieces  of  decaying  vegetable  matter  or  bits  of  bacte- 
rial zooglcea.  Remaining  in  contact 
with  these  helps  it  to  obtain  food.  The 
cilia  that  come  in  contact  with  the 
solid  cease  moving,  and  become  stiff 
and  set,  seeming  to  hold  the  Parame- 
cium against  the  object  (Fig.  45). 
Often  it  is  only  the  cilia  of  the  anterior 
end  that  are  thus  in  contact  and  im- 
movable; in  other  cases  cilia  of  the 
general  surface  of  the  body  show  the 
same  condition.  Meanwhile,  the  cilia 
of  the  oral  groove  continue  in  active 
motion,  so  that  a  rapid  current  passes 
from  the  anterior  end  down  the  groove 
to   the   mouth   (Fig.    46).      This    cur- 


FiG.  46.  —  Paramecium  at  rest  with 
anterior  end  against  a  mass  of  bacte- 
rial zooglcea  (a),  showing  the  currents 
produced  by  the  cilia. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  6 1 

rent  of  course  carries  many  of  the  bacteria  found  in  the  zooglcea  or 
on  the  decaying  plant  tissue ;  these  serve  as  food  for  the  animal.  The 
cilia  of  the  remainder  of  the  body  usually  strike  only  weakly  and 
ineffectively,  so  that  the  currents  about  the  Paramecium  are  almost  all 
due  to  the  movements  of  the  oral  cilia.  The  body  cilia  directly  behind 
those  in  contact  with  the  solid  are  usually  quite  at  rest. 

The  function  of  this  positive  contact  reaction  is  evidently,  under 
ordinary  conditions,  to  procure  food  for  the  animal.  But  Paramecium 
shows  no  precise  discrimination,  and  often  reacts  in  this  way  to  objects 
that  cannot  furnish  food.  Thus,  if  we  place  a  bit  of  torn  filter  paper 
in  the  water  containing  the  animals,  we  often  find  that  they  come  to 
rest  upon  this,  gathering  in  a  dense  group  on  its  surface,  just  as  they  do 
with  bits  of  bacterial  zooglcea  (Fig.  47).  The  oral  cilia  drive  a  strong 
current  of  water  to  the  mouth,  as  usual,  but  this  bears  no  food.  To 
bits  of  thread,  ravellings  of  cloth,  pieces  of  sponge,  or  masses  of  pow- 
dered carmine,  Paramecium  may  react 
in  the  same  way.  In  general  it  shows  a 
tendency  to  come  to  rest  against  loose  or 
fibrous  material;  in  other  words,  it  re- 
acts thus  to  material  with  which  it  can 
come  in  contact  at  two  or  more  parts  of 

the    body    at    once.        To     Smooth,     hard  Fig.    47.  —  Paramecia   gathered 

materials,  such  as  glass,  it  is  much  less      in  a  dense  mass  about  a  bit  of  filter 

.  paper. 

likely  to  react  in  this  manner,  so  that  it 

clearly  shows  a  certain  discrimination  in  this  behavior.  These  hard 
substances,  it  is  evident,  are  less  likely  to  furnish  food  than  the  soft 
fibrous  material  to  which  Paramecium  reacts  readily.  But  under  cer- 
tain conditions  Paramecium  comes  to  rest  even  against  a  smooth  glass 
surface,  or  against  the  surface  film  of  the  water.  Specimens  are  often 
found  at  rest  in  this  manner  in  the  angle  between  the  surface  film  of  a 
drop  of  water  and  the  glass  surface  to  which  it  is  attached. 

Paramecia  often  behave  in  the  manner  just  described  with  reference 
to  bodies  of  very  minute  size, —  to  small  bits  of  bacterial  zooglcea,  or 
to  a  single  grain  of  carmine.  Such  objects  are  of  course  too  small  to 
restrain  the  movements  that  naturally  result  from  the  activity  of  the  oral 
cilia  in  the  contact  reaction.  These  cilia  continue  to  beat  in  the  same 
manner  as  when  the  object  is  a  large  one,  producing  currents  similar  to 
those  shown  in  Fig.  46.  This  ciliary  motion  of  course  tends  to  drive 
the  animal  forward,  and  since  all  the  active  cilia  are  on  the  oral  side,  it 
tends  also  to  move  the  animal  toward  the  aboral  side.  The  resultant 
of  these  two  motions  at  right  angles  is  movement  in  the  circumference 
of  a  circle.     The  animal  moves  in  the  lines  of  the  water  currents  shown 


62 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


in  Fig.  46,  but  in  the  opposite  direction ;  it  is,  as  it  were,  whirled  about 
in  its  own  whirlpool.     The  resulting  path  is  shown  in  Fig.  48.     This 

circular  movement,  with  the  oral  side 
directed  toward  the  centre  of  the 
circle,  is  seen  only  in  specimens  show- 
ing the  contact  reaction  to  objects  of 
minute  size. 

The  contact  reaction  modifies 
strongly  the  reactions  to  most  other 
stimuli ;  this  is  a  matter  which  will 
be  taken  up  later. 

Thus  when  Paramecium  comes 
in  contact  with  a  solid  object,  it  may 
react  in  three  different  ways.  First, 
it  may  react  either  positively  or 
negatively,  this  depending  partly  on 
Fig.  48. —  Circular  path  followed  by    the  intensity  of  the  stimulus,  partly 

Paramecium  in  reacting  to  contact  with  a      Qn     h     physiological  condition   of  the 
minute  particle.  r    J  ° 

Paramecium.  If  it  reacts  negatively, 
this  reaction  may  take  either  one  of  two  forms.  If  the  stimulation 
occurs  at  the  anterior  end,  the  animal  gives  the  avoiding  reaction; 
if  it  occurs  elsewhere,  the  animal  merely  moves  forward. 


2.      REACTIONS  TO   CHEMICAL     STIMULI 

The  reactions  to  chemical  stimuli  occur  through  the  avoiding  reaction 
described  in  the  preceding  chapter.  As  we  have  seen,  the  avoiding 
reaction  is  produced  as  a  rule  by  a  change  from  one  chemical  to  another. 
With  regard  to  this  relation,  there  are  certain  facts  of  importance. 

In  all  cases  a  certain  amount  of  change  is  necessary  to  produce 
reaction ;  that  is,  the  chemical  must  be  present  in  a  certain  concentra- 
tion before  reaction  is  produced.  The  sensitiveness  of  different  indi- 
viduals varies  greatly,  and  even  that  of  given  individuals  changes  much 
with  changes  in  the  conditions.  It  is  therefore  not  possible  to  establish 
for  any  given  chemical  the  weakest  concentration  that  causes  the  avoid- 
ing reaction.  But  the  animals  when  in  ordinary  water  are  very 
sensitive  to  the  common  inorganic  chemicals,  reacting  to  very  weak  solu- 
tions. Thus  the  weakest  solutions  causing  reaction  have  been  found  to 
be  for  various  chemicals  about  as  follows :  — 

Sodium  chloride,  -^  to  ^.  per  cent  (-^  to  yg-Q  normal) ;  potassium 
bromate,  about  -^  per  cent ;  sodium  carbonate,  about  -^jTo  to  3TT0  Per 
cent ;  copper  sulphate,  about  -g-^g-  per  cent ;  potassium  hydroxide,  about 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  63 

2^  per  cent ;  sodium  hydroxide,  5-^y  per  cent ;  sulphuric  acid,  -g-^-Q-  per 
cent  of  an  ordinary  laboratory7  solution  ;  hydrochloric  acid,  g  jj-q  per  cent 
of  the  usual  solution ;  alcohol,  1  per  cent ;  chloral  hydrate,  -§  per  cent. 
For  the  inorganic  chemicals,  many  of  these  solutions  are  so  weak  as  not 
to  affect  at  all  the  sense  of  taste  in  man. 

Is  the  reaction  of  Paramecium  to  solutions  due  to  the  chemical 
properties  of  the  dissolved  substance,  or  to  its  osmotic  pressure  ?  This 
question  may  be  answered  from  the  data  which  we  possess  (partly 
given  above)  as  to  the  weakest  solutions  which  cause  reactions.  If 
the  reactions  are  due  to  osmotic  pressure,  then  solutions  having  equal 
osmotic  pressure  must  have  equal  stimulating  power.  The  results  of 
the  experiments  on  the  weakest  solutions  necessary  to  cause  reaction 
show  that  this  is  not  true.  Thus,  if  the  osmotic  pressure  of  a  solution 
of  sodium  chloride  that  will  barely  cause  the  reaction  is  taken  as  unity, 
the  osmotic  pressures  of  solutions  of  a  number  of  other  substances  hav- 
ing the  same  stimulating  effect  are  as  follows :  potassium  bromate,  ^ ; 
sodium  carbonate,  -^  5  copper  sulphate,  217-3  5  potassium  hydroxide,  -^-q  ! 
sulphuric  acid,  -^  5  ethyl  alcohol,  8.  The  stimulating  effect  is  not  then 
proportional  to  the  osmotic  pressure,  and  must  be  due  to  the  chemical 
properties  of  the  substances  in  solution. 

This  is  further  shown  by  the  fact  that  Paramecia  will  enter  solu- 
tions of  sugar  and  of  glycerine  having  osmotic  pressure  many  times  as 
great  as  that  of  a  solution  of  sodium  chloride  which  they  avoid.  They 
swim  into  a  20  per  cent  solution  of  sugar  or  a  10  per  cent  solution  of 
glycerine  without  reaction.  The  solutions  are  so  concentrated  that 
they  cause  plasmolysis;  the  Paramecia  shrink  into  flattened  plates. 
Just  as  the  shrinking  becomes  evident  to  the  eye  of  the  observer,  the 
Paramecia  react  in  the  usual  way,  by  swimming  backward  and  turn- 
ing towards  the  aboral  side.  But  this  is  as  a  rule  too  late  to  save  them, 
and  they  die  in  the  dense  solution.  Thus  it  is  evident  that  osmotic  press- 
ure, acting  by  itself,  produces  the  same  "avoiding  reactions"  as  do 
other  stimuli,  but  the  result  is  not  produced  till  the  Paramecia  are 
already  injured  beyond  help.  The  reactions  to  most  solutions  are  then 
clearly  due  to  their  chemical  properties. 

Is  the  avoiding  reaction  that  is  produced  by  chemicals  due  directly 
to  the  injuriousness  of  the  substance?  This  question  may  be  answered 
by  a  series  of  experiments  based  on  a  method  similar  to  that  used  in 
determining  whether  the  reaction  is  due  to  osmotic  pressure.  If  the 
reaction  is  due  to  the  injuriousness  of  the  chemicals,  then  two  substances 
which  are  equally  injurious  must  have  equal  powers  of  inducing  reac- 
tion ;  in  other  words,  the  repelling  powers  of  any  two  substances  must 
be  proportional  to  their  injurious  effects. 


64 


BEHAVIOR   OF    THE   LOWER    ORGANISMS 


An  extensive  series  of  experiments  has  shown  that  this  is  not  true 
(Jennings,  1899  c;  Barratt,  1905).  We  may  compare,  for  example,  the 
effects  of  chromic  acid  and  of  potassium  bichromate.  The  weakest 
solution  of  the  former  which  kills  the  Paramecia  in  one  minute  is  ^-ifo 
per  cent;  the  weakest  solution  of  the  latter  having  the  same  effect  is 
1  per  cent.  Hence  the  chromic  acid  is  150  times  as  injurious  as  the 
potassium  bichromate. 

On  the  other  hand,  the  weakest  solution  of  chromic  acid  that  sets 
in  operation  the  avoiding  reaction  is  still  j^-q  per  cent,  while  potassium 
bichromate  has  the  same  effect  in  a  -^  per  cent  solution.  The  repel- 
lent power  is  thus  not  proportional  to  the  injurious  effects;  the  potas- 
sium bichromate  is  repellent  in  a  strength  -^  that  which  is  immediately 
injurious,  which  chromic  acid  does  not  repel  until  it  has  reached  a 
strength  that  is  already  destructive.  Similar  relations  are  found  for 
other  pairs  of  substances.  Thus  the  stimulating  power  of  sodium 
chloride  is  ten  times  that  of  cane  sugar,  in  proportion  to  its  injuriousness. 

Comparing  a  large  number  of  chemicals  from  this  point  of  view, 
it  has  been  found  that  they  may  be  divided  into  two  classes.  On  the 
one  hand  are  a  number  of  substances  which  must  be  classified  with 
potassium  bichromate  and  sodium  chloride,  because  their  stimulating 
power  is  strong  in  proportion  to  their  injurious  effects.  Paramecia 
avoid  these  substances  markedly ;  if  a  drop  of  a  strong  solution  of  one 
of  them  is  introduced  into  a  preparation  of  the  infusoria,  it  remains 
empty,  and  none  of  the  infusoria  are  killed  by  it.  On  the  other  hand, 
there  is  a  large  number  of  substances  which,  like  chromic  acid  and 
sugar,  produce  stimulation  only  where  they  are  strong  enough  to  be 
immediately  injurious.  When  a  strong  solution  of  one  of  these  is  brought 
into  a  preparation  of  Paramecia,  it  proves  very  destructive,  for  the  ani- 
mals as  a  rule  do  not  react  until  they  have  been  injured.  The  follow- 
ing table  (from  Jennings,  1899  c)  shows  the  distribution  of  various 
chemicals  from  tills  point  of  view  :  — - 


TABLE 


r.  Repellent  power  strong  in  proportion 
to  injurious  effects  ;  reaction  protective. 

LiCl,  NaCl,  KC1,  CsCl, 

Li  Br,  NaBr,  KBr,  RuBr, 

Lil,  Nal,  KI.  Rul, 

Li.,CO.,,  Na.,CO„  KXO,, 

LiNO.,',  NaNOg,  KNO., 

NaOH,  KOH.NaF,  KF. 

NH4F,  NH4C1.  NH4Ur,  NH4I, 

CaCl.,,  SrCl,,  BaCL, 

Ca(NO,),„  Sr(N03)2,  Ba(NO,).„ 
Potassium  bromate,  Potassium    perman- 
ganate, Potassium  bichromate.  Potassium 
rerricyanide,  Ammonium  bichromate. 


2.  Repellent  power  very  weak  in  pro- 
portion to  injurious  effects  ;  reaction  not 
completely  protective. 

HF,  HC1.  HBr.  HI.  H,S04,  HNO„ 
Acetic  acid,  Tannic  acid.  Picric  acid. 
Chromic  acid.  Ammonia  alum,  Ammonio- 
ferric  alum.  Chrome  alum.  Potash  alum, 
CuS04,  CuCl,,  ZnCl,,  HgCl,,  A1C1,,  Cop- 
per acetate.  Cane  sugar,  Lactose.  Maltose, 
Dextrose,  Mannite,  Glycerine,  Urea. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  6$ 

This  table  shows  that  the  relative  repellent  power  of  different  sub- 
stances bear  a  somewhat  definite  relation  to  their  chemical  composi- 
tion. All  alkalies  and  compounds  of  the  alkali  and  the  earth  alkali 
metals  (save  the  alums,  where  the  proportion  of  the  metals  is  very  small) 
have  a  relatively  strong  repellent  effect ;  most  other  compounds  have  not. 

While  our  general  result  is  that  the  stimulating  powers  of  different 
chemicals  are  not  proportional  to  their  injurious  effects,  yet  one  further 
fact  of  importance  comes  out  clearly.  All  substances,  whatever  their 
nature,  do  produce,  as  soon  as  they  become  injurious,  the  avoiding 
reaction.  With  all  the  substances  in  the  second  column  the  avoiding 
reaction  is  produced  when  a  strength  sufficient  to  be  injurious  is  reached 
and  the  reaction  seems  clearly  due  to  the  injuries  produced.  The 
significance  of  this  fact  will  be  discussed  later. 

In  the  chapter  preceding  the  present  one,  we  have  seen  that  Para- 
mecia  collect  in  certain  chemicals,  owing  to  the  fact  that  passage  out 
of  these  causes  the  avoiding  reaction.  The  two  chief  classes  of  chemi- 
cals in  which  the  animals  collect  are  acids  and  oxygen. 

Paramecia  collect  in  all  weakly  acid  solutions,  no  matter  what  acid 
substance  is  present.  Sulphuric,  hydrochloric,  nitric,  hydriodic,  and 
many  other  inorganic  acids;  acetic,  formic,  carbonic,  propionic,  and 
other  organic  acids,  have  been  tested,  and  the  animals  have  been  found 
to  gather  in  all.  The  Paramecia  collect  even  in  solutions  of  poisonous 
acid  salts,  such  as  corrosive  sublimate  and  copper  sulphate,  where  they 
are  quickly  killed.  In  all  these  cases  they  swim  into  the  solution  with- 
out reaction,  but  give  the  avoiding  reaction  at  passing  out.  They 
give  the  avoiding  reaction  also  after  the  injurious  chemical  begins  to 
act  on  them,  but  under  the  circumstances  this  does  not  save  them  from 
destruction. 

It  seems  remarkable  that  the  animals  should  thus  tend  to  gather  in 
acids,  when,  as  is  well  known,  the  decaying  vegetable  infusions  in  which 
they  live  are  usually  alkaline  in  character. 
Specimens  in  water  that  is  decidedly  alka- 
line collect  even  more  readily  in  acids  than 
do  those  in  a  neutral  fluid. 

A  solution  may  contain  both  an  acid 
and  a  repellent  substance,  as  when  ^g-  per 
cent  acetic  acid  is  mixed  with  \  per  cent  fig.  49.  -  Collection  of  Para- 

Sodium    chloride.      In    this    Case    a    CUrioUS       mecia    about    the    periphery    of    a 

effect  is  produced.     The  Paramecia  gather     mixture  of  salt  and  acid- 
in  a  ring  about  the  outer  edge  of  the  solution,  as  in  Fig.  49.     They  are 
repelled  both  by  the  inner  fluid  and  the  surrounding  water.     The  path 
of  a  Paramecium  in  such  a  ring  is  similar  to  that  shown  in  Fig.  50. 


66  BEHAVIOR   OF   THE  LOWER  ORGANISMS 

Strong  acid  solutions  cause  the  avoiding  reaction  as  do  other  chemi- 
cals. If  a  drop  of  strong  acid  solution  is  introduced  into  a  preparation 
of  Paramecia,  the  animals  collect  about  its  periphery,  where  the  acid 
is  diluted  by  the  surrounding  water,  just  as  in  Fig.  49.  Individuals 
which  swim  against  the  inner  strong  acid  respond  by  giving  the  avoid- 
ing reaction  in  a  very  pronounced  way,  —  swim- 
ming far  backward  and  turning  toward  the  aboral 
side,  for  perhaps  two  or  three  or  more  complete 
turns.  They  react  also  at  the  outer  boundary  of  the 
acid  ring,  so  that  within  the  ring  the  individual 
Paramecium  follows  such  a  path  as  is  shown  in 

Fig.  5°- 

Often  the  reaction  is  not  produced  at  the  inner 
•   ,Fl?"  51°-7Patho.an  boundary  of  the  ring,  by  the  strong  acid,  until  the 

individual     Paramecium  J  °'      J  . 

in  such  a  ring  as  is  shown  Paramecium  has  entered  far  enough  to  be  injured, 
in  Fig.  49.  or  even  killed.     A  drop  of  strong  acid  introduced 

into  a  preparation  is  usually  soon  surrounded  by  a  zone  of  dead 
animals.  Acids,  as  we  have  seen  (p.  64),  belong  with  those  substances 
which  do  not  produce  the  avoiding  reaction  till  they  have  become 
directly  injurious. 

Paramecia  do  not,  under  usual  conditions,  collect  in  oxygen.  If 
we  introduce  an  air  bubble  or  a  bubble  of  oxygen  into  a  slide  prepara- 
tion of  Paramecia,  they  do  not  as  a  rule  collect  about  it.  But  if  the 
outer  air  is  excluded  from  this  preparation  by  covering  its  edges  with 
vaseline,  and  it  is  allowed  to  stand  for  a  long  time,  the  behavior  changes. 
The  oxygen  has  of  course  become  nearly  exhausted  and  now  the  Para- 
mecia gather  about  the  air  or  the  oxygen.  The  collections  are  formed 
in  exactly  the  same  way  as  are  those  in  acids. 

Thus  the  experiments  show  that  all  reactions  to  chemicals  take  place 
through  the  avoiding  reaction,  and  this  reaction  is  produced  by  a  change 
in  the  intensity  of  action  of  the  chemical  in  question.  With  some  chem- 
icals, or  under  certain  conditions,  it  is  a  change  to  a  greater  intensity 
that  produces  the  avoiding  reaction ;  in  other  cases  it  is  a  change  to  a 
less  intensity  that  produces  the  reaction.  With  acids  both  an  increase 
and  a  decrease  beyond  a  certain  intensity  produce  reaction.  We  may 
express  the  facts  for  all  chemicals  in  the  following  general  way.  For 
each  chemical  there  is  a  certain  optimum  concentration  in  winch  the 
Paramecia  are  not  caused  to  react.  Passage  from  this  optimum  to 
regions  of  either  greater  or  less  concentration  causes  the  avoiding  reac- 
tion, so  that  the  animals  tend  to  remain  in  the  region  of  the  optimum, 
and  if  this  region  is  small,  to  form  here  a  dense  collection.  For  acids 
and  for  oxygen  the  optimum  is  a  certain  very  low  concentration.     For 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


67 


most  other  chemicals  the  optimum  is  zero ;  an  increase  in  intensity  by 
any  effective  quantity  produces  the  avoiding  reaction,  while  decrease  in 
intensity  has  no  effect.  Hence  the  Paramecia  tend  to  collect  where  none 
of  the-  chemical  is  present. 

The  point  needs  to  be  brought  out  clearly  that  it  is  not  merely  pas- 
sage from  the  absolute  optimum  that  induces  reaction,  but  passage  in 
a  direction  leading  away  from  the  opti- 
mum. To  constant  conditions,  even  when 
not  optimal,  Paramecium  becomes  ac- 
climatized ;  it  may  live  for  example  in  a 
jJq  per  cent  salt  solution,  though  pas- 
sage from  water  to  this  causes  reaction. 
While  in  this  salt  solution,  passage  into 
conditions  lying  still  farther  from  the 
optimum,  as  into  \  per  cent  salt  solu- 
tion, causes  the  avoiding  reaction,  while 
passage  to  conditions  lying  nearer  the 
optimum  produces  no  reaction.  Ac- 
climatization to  non-optimal  conditions 
is  an  ever  present  factor  in  the  behavior 
of  the  organisms.  This  is  another  way 
of  stating  the  fact  that  change  is  the 
chief  factor  inducing  reactions. 

Acids  then  take  a  peculiar  position 
among  chemicals  merely  in  the  fact  that 
a  certain  positive  concentration  forms 
the  optimum,  passage  to  a  lower  con- 
centration inducing  reaction.  The  pe- 
culiar behavior  of  Paramecium  with 
respect  to  acids  plays  a  large  part  in 
its  life  under  natural  conditions.  Paramecia  produce  carbon  dioxide 
in  their  respiratory  processes  as  do  other  organisms.  This  substance 
when  dissolved  in  water  produces  an  acid  solution,  the  acidity  being 
due  to  carbonic  acid.  In  such  a  solution  Paramecia  gather  as  in 
other  acids.  This  may  be  shown  by  introducing,  by  means  of  a  capil- 
lary pipette  attached  to  a  rubber  bag  containing  the  gas,  a  small 
bubble  of  carbon  dioxide  into  a  slide  preparation  of  Paramecia.  The 
infusoria  quickly  gather  in  a  dense  collection  about  the  bubble,  at  first 
pressing  closely  against  it  (Fig.  51,  ,4).  Later  the  Paramecia  spread 
out  with  the  diffusion  of  the  carbon  dioxide  (B).  After  a  time  the  ani- 
mals are  usually  found  chiefly  about  the  margin  of  the  area  containing 
the  carbon  dioxide  (C). 


Fig.  51.  —  Collection  of  Paramecia 
about  a  bubble  of  CO-t.  a  is  a  bubble  of 
air,  b  of  CO2.  A  shows  the  preparation 
two  minutes  after  the  introduction  of  the 
CO2;  B,  two  minutes  later;  C,  eighteen 
minutes  later. 


68 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


'->•'.:?' 


'V-:: 


Now,  the  Paramecia  gather  in  the  solution  of  carbon  dioxide  pro- 
duced by  themselves,  just  as  in  that  due  to  other  causes.  In  this  way 
dense  spontaneous  groups  are  formed,  in  which  the  phenomena  seen 
in  the  collections  about  bubbles  of  carbon  dioxide  are  reproduced.  If 
a  large  number  of  Paramecia  are  mounted  in  water  on  a  slide,  they  do 
not  remain  scattered,  but  soon  gather  in  one  or  more  regions  (Fig.  52). 
Within  such  groups  the  individuals  move  about  in  all  directions.  On 
coming  to  an  invisible  outer  boundary,  they  give  the  avoiding  reaction 
in  a  mild  form,  so  that  they  do  not  leave  the  group.  The  area  covered 
by  the  group  does  not  remain  of  the  original  size,  but  slowly  enlarges, 
as  shown  in  Fig.  52.  It  continues  thus  to  increase  in  size  until  it  covers 
the  whole  preparation. 

By  the  use  of  proper  indicators  it  can  be  shown  that  such  spontane- 
ous groups  contain  an  acid,  and  this  is  beyond  doubt  due  to  the  carbon 

dioxide  known  to  be  produced  in  res- 
piration. The  groups  are  formed  in 
the  following  way.  Two  or  three  Para- 
mecia by  chance  strike  against  some 
small,  loose  object,  a  roughening  of  the 
surface  of  the  glass,  or  the  like,  and 
come  to  rest,  in  the  way  described  in 
our  account  of  the  reaction  to  mechan- 
ical stimuli.  They  of  course  produce 
Q        (•'.**".         .".V5     /.'•'  carbon  dioxide,  which  diffuses  into  the 

surrounding  water.  Other  Paramecia 
that  swim  by  chance  across  this  area  of 
carbon  dioxide  of  course  stop  and  re- 
main. They  too  produce  carbon  diox- 
ide, so  that  the  area  grows  in  size ;  more 
Paramecia  enter  it,  and  finally  a  large 
and  dense  collection  is  formed.  The 
area  occupied  by  such  a  collection  con- 
tinually increases  in  size,  because  the 
Fig.  52.— Spontaneous  groups  formed  Paramecia  continue  to  produce  carbon 

by  Paramecia.    A ,  B,  C,  successive  stages    ..       .  .  .       .  .  .  .._ 

in  the  spreading  out  of  such  groups.         dioxide,  and    this  continues   to   diffuse 

through  the  water. 
The  tendency  of  Paramecia  to  gather  in  regions  containing  carbon 
dioxide  plays  a  large  part  in  their  life  under  natural  conditions,  and 
this,  together  with  the  fact  that  they  themselves  produce  carbon  dioxide, 
explains  many  peculiar  phenomena  in  their  behavior.  When  placed  in 
tubes  or  vessels  of  any  kind,  Paramecia  usually  show  a  tendency  to 
collect  into  groups  or  clouds,  having  a  definite  boundary  (Fig.   53). 


'.-;-**"  .,..•.".->•■:•. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


69 


iW 


B 


This  is  of  course  a  result  of  their  reaction  to  carbon  dioxide  produced 
by  themselves.  In  all  experimental  work  on  the  reactions  of  these 
organisms  to  stimuli  it  is 
necessary  to  take  these  |V__> 
facts  into  account.  For 
example,  in  order  to  get 
clear  results  in  such 
work,  Param  ecia  must  not 
be  taken  with  a  pipette 
directly  from  a  dense 
collection  in  a  culture 
jar,  and  at  once  mounted 
on  a  slide.  Such  col- 
lections contain  carbon 
dioxide,  which  may  be- 
come unequally  distrib- 
uted throughout  the 
preparation,  as  a  result 
of  the  fact  that  some  of 
the  water  outside  the 
collection  is  likely  to  be 
taken  up  with  the  pi- 
pette at  the  same  time. 
The  Paramecia  quickly 
gather  in  the  region  containing  most  carbon  dioxide,  and  their  reac- 
tions to  other  substances  are  inconstant  and  irregular,  owing  to  the 
interference  due  to  the  reaction  to  carbon  dioxide  (Fig.  53,  B).  For 
experimental  work  it  is  always  necessary  before  each  experiment  to 
place  a  few  drops  of  the  water  containing  the  Paramecia  in  the  bot- 
tom of  a  shallow  watch-glass,  and  to  aerate  it  thoroughly  by  stirring  it 
and  bringing  it  into  contact  with  the  air  by  means  of  the  pipette. 
Then  this  aerated  water  and  its  contained  Paramecia  must  be  used  for 
the  experiments.  This  aeration  must  be  repeated  before  each  experi- 
ment, and  the  test  for  the  reaction  to  other  chemicals  must  be  made 
immediately  after  the  Paramecia  are  mounted,  before  they  have  had 
time  to  produce  an  appreciable  quantity  of  carbon  dioxide.  If  these 
precautions  are  neglected,  the  reactions  of  the  Paramecia  are  incon- 
stant, and  the  results  of  experiments  are  likely  to  be  very  misleading. 
Paramecia  in  a  solution  of  carbon  dioxide  react  to  other  agents  in  a 
manner  entirely  different  from  the  reaction  of  individuals  in  water  not 
containing  carbon  dioxide.  The  account  of  their  reactions  given  in 
the  present  chapter  assumes  that  the  carbon  dioxide  has  been  in  every 


Fig.  53.  — Spontaneous  collections  of  Paramecia,  due  to 
COo.  A,  Collections  formed  in  an  upright  tube,  after  Jensen. 
B,  Collection  formed  beneath  a  cover-glass,  when  water  is 
taken  directly  from  a  dense  culture  of  Paramecia.  C,  Collec- 
tion in  the  bottom  of  a  watch-glass. 


70  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

case  removed   from   the  water.      The  experimental  results  described 
cannot  be  verified  unless  this  is  done. 

In  general  it  cannot  be  too  much  emphasized  that  in  all  experimental 
studies  on  the  behavior  of  Paramecium  close  attention  to  their  reac- 
tions with  reference  to  carbon  dioxide  is  necessarv.  When  inconstant 
results  are  obtained,  or  results  seeming  to  contradict  those  noted  by 
other  observers,  it  will  often  be  found  that  inattention  to  the  carbon 
dioxide  produced  by  the  animals  is  at  the  bottom  of  the  difficulty. 

3.      REACTIONS    TO    HEAT    AND    COLD 

As  we  saw  in  the  preceding  chapter,  a  change  to  a  temperature  de- 
cidedly above  or  decidedly  below  the  optimum  causes  Paramecia  to 
give  the  avoiding  reaction,  while  a  change  leading  toward  the  optimum 
does  not.  As  a  result  the  animals  collect  in  temperatures  as  near  the 
optimum  as  possible. 

The  effects  of  heat  and  cold  differ  slightly,  since  heat  increases  the 
rapidity  of  movement,  while  cold  reduces  activity.  Both  produce  the 
avoiding  reaction  in  the  same  way,  but  in  heated  water  the  reaction  is 
continued  violently  till  the  animals  escape  or  are  killed,  while  in  ice 
water  the  animals  after  a  time  become  benumbed  and  sink  to  the  bottom. 

The  reactions  to  heat  and  cold  are  seen  in  a  striking  way  when  the 
Paramecia  are  placed  in  a  long  tube  or  trough,  one  end  of  which  is  heated 
while  the  other  is  maintained  at  the  normal  temperature,  or  is  cooled. 
The  Paramecia  then  pass  to  the  region  that  is  nearest  the  optimum, 
forming  here  a  collection.  By  changing  the  temperature  of  the  ends 
or  of  the  middle,  the  Paramecia  may  be  driven  from  one  end  to  the  other 
or  caused  to  gather  in  any  part  of  the  trough.  Such  experiments  were 
devised  by  Mendelssohn  (1895,  1902,  1902  a,  b).  He  passed  tubes 
beneath  the  middle  and  ends  of  the  trough  or  slide  bearing  the  animals, 
and  through  these  tubes  he  conducted  water  of  different  temperatures. 
By  changing  the  connections  of  the  tubes,  that  end  of  the  trough  which 
is  at  first  heated  may  later  be  cooled,  etc.,  without  disturbing  the  ani- 
mals in  any  other  way.1 

If  in  this  way  we  heat  the  water  at  one  end  of  the  trough  to  38  degrees 
while  we  cool  the  opposite  end  to  10  degrees,  the  Paramecia  collect  in 
an  intermediate  region.  By  varying  the  temperatures  at  the  two  ends, 
the  infusoria  may  be  driven  back  and  forth,  as  represented  in  Fig.  54, 
taken  from  Mendelssohn.  By  grading  the  temperatures  properly, 
the  sensitiveness  of  Paramecium  to  changes  in  temperature  may  be 
measured,  and  the  optimum  temperature  determined  very  accurately. 

1  A  simple  apparatus  of  this  sort  is  described  and  figured  in  Jennings,  1904. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


71 


Mendelssohn  found  that  the  optimum  temperature  for  Paramecium 
lies,  under  ordinary  conditions,  between  24  and  28  degrees  C, 
and  that  when  there  is  a  difference  of  but  3  degrees  C.  between  the 
two  ends  of  a  trough  10  centimeters  in  length,  the  Paramecia  gather 
at  the  end  of  the  trough 
nearest  the  optimum 
(see  Fig.  54).  If  the 
end  a  has  a  tempera- 
ture of  26  degrees,  the 
end  b  38  degrees,  the 
Paramecia  gather  at 
the  end  a;  if  now  the 
temperature  of  the  two 
ends  is  interchanged, 
the  Paramecia  travel 
from  a  toward  b,  and 
collect  there.  The 
same  results  are  pro- 
duced if  one  end  has 
a   temperature   of    10 

degrees,    the    Other    of  Fig.    54.  —  Reactions  of   Paramecia  to  heat  and   cold,  after 

26    de°TeeS     save    that    Mendelssohn  (1902).    At  a  the  infusoria  are  placed  in  a  trough, 

both  ends  of  which  have  a  temperature  of  19  degrees.  They  are 
equally  scattered.  At  b  the  temperature  of  one  end  is  raised  to 
38  degrees  while  the  other  is  only  26  degrees.  The  infusoria  col- 
lect at  the  end  having  the  lower  temperature.  At  c  one  end  has 
a  temperature  of  2  5  degrees,  while  the  other  is  lowered  to  1  o  degrees. 
If  Para-  '^^le  arumals  now  collect  at  the  end  having  the  higher  tempera- 
ture. 


a 

19"-                                                        19°- 

l 

^Bl 

26°~                   - —                               38- 

c 

•^Srrl^/f^^M 

10- 


25- 


in  this  case  the  Para- 
mecia gather  at  the 
end  having  the  higher 
temperature, 
mecia  are  kept  for 
some  hours  at  a  temperature  of  36  to  38  degrees,  the  optimum  be- 
comes higher,  —  about  30  to  32  degrees;  otherwise  the  phenomena 
remain  the  same. 

Observation  of  the  movement  of  the  individuals  shows  that  the  re- 
actions in  these  experiments  take  place  in  the  following  manner.  As  one 
end  of  the  trough  is  heated  above  the  optimum,  the  Paramecia  in  that 
region  are  seen  to  become  more  active,  darting  about  rapidly  in  all  direc- 
tions. Those  that  come  against  the  sides  or  end  of  the  vessel  respond  by 
the  avoiding  reaction ;  they  are  thus  directed  elsewhere.  Individuals 
that  are  swimming  toward  the  hotter  region  likewise  give  the  avoiding 
reaction,  —  at  first  in  but  a  slightly  marked  form,  stopping,  swinging 
the  anterior  end  about  in  a  circle,  as  illustrated  in  Figs.  37-39,  and  "try- 
ing" forward  movement  in  a  number  of  different  directions.  This  con- 
tinues as  long  as  they  are  moving  toward  the  warmer  region;  but  as 
soon  as  their  direction  of  movement  leads  them  toward  the  cooler  region, 


72  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

the  avoiding  reaction  ceases,  and  they  continue  to  swim  in  that  direc- 
tion. At  that  end  of  the  trough  which  is  cooled  below  the  optimum, 
similar  effects  are  produced,  save  that  the  reaction  is  less  rapid,  and  the 
Paramecia  therefore  leave  this  region  much  more  slowly  than  they  do 
the  heated  end. 

Thus  after  a  time  the  direction  of  movement  of  all  the  individuals  in 
the  hot  or  cold  end  of  the  trough  has  become  changed,  and  all  are  moving, 
often  in  a  well-defined  group,  toward  the  optimum  region.  Thus  we 
may  observe  in  these  temperature  reactions  a  well-defined  common 
orientation  of  a  large  number  of  organisms ;  all  are  headed  toward  the 
optimum.  This  orientation  is  brought  about,  as  we  have  seen,  by  ex- 
clusion. That  is,  movement  in  any  other  direction  is  stopped,  through 
the  production  of  the  avoiding  reaction,  so  that  all  finally  travel  in  this 
one  direction.  Or,  to  put  it  more  accurately,  the  Paramecia  try  every 
possible  direction,  through  the  avoiding  reaction  (Figs.  37-39),  till 
finally  they  all  find  the  only  one  which  does  not  cause  stimulation;  in 
this  direction  they  continue  to  move.  The  method  of  reaction,  by 
systematic  trial  of  all  directions,  is  such  as  to  find  any  existing  avenue 
of  escape,  no  matter  how  narrow  it  may  be. 


4.      REACTION  TO   LIGHT 

To  ordinary  visible  light  Paramecium  is  not  known  to  react  in  any 
way.  If  light  is  allowed  to  fall  on  the  animals  from  one  side  only,  or 
if  one  portion  of  the  vessel  containing  them  is  strongly  righted  while  the 
rest  is  shaded,  this  has  no  observable  effect  on  their  movements  or 
distribution. 

But  Hertel  (1904)  has  recently  shown  that  to  powerful  ultra  violet 
light  Paramecium  does  react.  The  ultra  violet  rays  employed  by  Hertel 
came  from  a  magnesium  spectrum ;  they  were  of  a  wave  length  of 
280  fifx.  When  part  of  a  drop  of  water  containing  Paramecia 
was  subjected  to  this  light,  the  animals  in  the  lighted  region  at  once 
began  to  move  about  rapidly.  They  therefore  passed  quickly  into 
the  region  not  lighted.  Specimens  moving  about  in  this  shaded  region 
stopped  at  once  on  reaching  the  boundary  of  the  lighted  area,  and  turned 
away.  It  is  evident  that  the  reaction  to  light  is  by  the  usual  avoiding 
reaction,  though  the  details  of  the  movement  were  not  observed  by 
Hertel. 

When  the  animals  were  unable  to  escape  from  the  light,  their  move- 
ment became  uncoordinated,  and  in  ten  to  fifty  seconds  it  ceased.  The 
animals  were  dead. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  73 

5.      ORIENTING     REACTIONS,    TO    WATER     CURRENTS,    TO    GRAVITY,    AND 

TO    CENTRIFUGAL    FORCE 

In  the  reactions  which  we  have  thus  far  considered,  the  infusoria  do 
not  become  oriented  in  any  precise  way  with  relation  to  the  direction  of 
action  of  the  stimulating  agent.  But  to  water  currents,  to  gravity,  and 
to  centrifugal  force  the  animals  at  times  react  in  such  a  way  as  to  bring 
about  a  definite  orientation,  with  the  body  axis  of  all  the  reacting 
individuals  in  line  with  the  external  force.  In  a  water  current  the 
anterior  end  is  directed  up  stream ;  under  the  influence  of  gravity  the 
anterior  end  is  directed  upward,  while  when  subjected  to  a  centrifugal 
force  the  anterior  end  is  directed  against  the  action  of  the  force. 

How  are  these  results  produced,  and  why  do  the  organisms  take  a 
definite  axial  orientation  under  the  action  of  these  stimuli,  while  they  do 
not  under  most  other  stimuli  ? 

In  the  reactions  to  water  currents  and  to  gravity,  direct  observation 
has  shown  that  the  orientation  is  produced  through  the  movements 
which  we  have  called  the  avoiding  reaction.  Under  the  action  of  a 
centrifugal  force,  observation  of  individuals  is  impossible,  but  beyond 
doubt  the  reaction  is  the  same  as  that  due  to  gravity. 

A.    Reactions  to  Water  Currents 

The  reactions  to  water  currents  can  best  be  studied  in  a  tube  like 
that  shown  in  Fig.  55.  By  covering  the  two  open  ends  with  rubber  caps 
filled  with  air,  and 
pressing  on  these,  the 
water  containing  the 

animals    in    the   tube  Fig.  55. — Tube  used  in  studying  the  reactions  to  water  cur- 

can  be  driven  through 

the  narrow  part  of  the  tube  with  any  desired  velocity.  With  a  certain 
velocity  of  current  most  of  the  individuals,  both  those  that  are  free 
swimming  and  those  that  are  resting  against  the  glass,  are  seen  to 
place  themselves  in  line  with  the  current,  with  anterior  end  up  stream. 
Some  of  the  individuals  usually  do  not  react.  In  those  that  do,  the 
reaction  is  brought  as  follows :  As  soon  as  the  current  begins  to  act, 
producing  a  disturbance  in  the  water,  the  animals  give  the  avoiding 
reaction  in  a  not  very  pronounced  form.  That  is,  a  given  individual 
swims  more  slowly  or  stops,  and  swerves  more  strongly  toward  the 
aboral  side,  thus  swinging  the  anterior  end  about  in  a  circle,  as  in 
Figs.  37  and  38,  "trying"  various  directions.  It  then  starts  forward 
again  in  one  of  these  directions.  This  reaction  may  be  repeated  sev- 
eral times,  till  the  infusorian  finally  comes  into  a  position  with  anterior 


74  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

end  directed  up  stream.  The  reaction  then  ceases,  and  the  infusorian 
remains  in  this  position,  either  swimming  forward  against  the  current, 
or  at  rest  against  the  wall  of  the  tube.  Sometimes  the  reaction  is  a 
little  more  precise,  the  animal  turning  directly  toward  the  aboral  side 
till  the  anterior  end  is  directed  up  stream.  This  is  commonly  the 
case  with  the  individuals  that  are  at  rest  against  a  solid.  The  reaction 
of  the  resting  specimens  is  less  easily  observed,  for  the  current  easily 
carries  them  away  from  their  attachment,  when  of  course  they  behave 
like  other  free  specimens. 

What  is  the  cause  of  the  reaction  to  water  currents  ?  Under  natural 
conditions  the  cilia  of  Paramecium  are  beating  backward,  driving  a  cur- 
rent of  water  backward  over  the  surface,  especially  in  the  oral  groove. 
If  an  external  current  moves  in  the  opposite  direction,  or  in  some  oblique 
direction,  it  will  of  course  act  in  opposition  to  the  cilia  on  that  part  of 
the  body  which  it  strikes,  tending  to  reverse  or  disarrange  them,  and  to 
reverse  or  change  the  direction  of  the  usual  currents.  It  appears  not 
surprising  that  such  a  disturbance  acts  as  a  stimulus,  causing  the  usual 
avoiding  reaction  until  the  disturbance  is  corrected.  The  correction  can 
occur  only  when  the  animal  is  headed  up  stream ;  the  current  is  then 
passing  backward  over  the  body  in  the  usual  direction.  The  reaction 
is  essentially  a  response  to  a  mechanical  disturbance,  comparable  to  that 
due  to  the  touch  of  a  solid  body. 

If  this  is  the  correct  explanation,  as  seems  probable,  then  there  should 
be  no  reaction  when  the  animal  is  completely  immersed  in  a  homogene- 
ous current,  —  one  moving  at  the  same  velocity  in  all  parts.  For  as 
Lyon  (1904)  has  pointed  out,  under  these  circumstances  the  animal  is 
merely  transferred  bodily  in  a  certain  direction,  along  with  the  medium 
surrounding  it,  and  at  the  same  rate.  Its  relation  to  the  enveloping  fluid 
is  the  same  as  in  quiet  water;  there  is  nothing  to  cause  a  disturbance. 
"Stimulation  implies  a  change  of  relation  between  organism  and  en- 
vironment. But  if  both  in  all  their  parts  are  moving  at  the  same  veloc- 
ity, their  relations  do  not  change,  and  the  conditions  for  stimulation  are 
wanting"  (Lyon,  1904,  p.  150). !  The  animal  should  then  react  only 
when  either  it  is  in  contact  on  one  side  with  a  solid,  or  when  the  current 
is  moving  more  rapidly  on  one  side  than  on  the  other,  producing  a  shear- 
ing effect,  with  the  necessarily  accompanying  disturbing  action.  Whether 
this  is  true  or  not  is  very  difficult  to  determine,  but  observation  seems  to 
indicate  that  it  is. 

1  This  consideration,  as  well  as  the  fact  that  individuals  resting  against  a  surface 
react  to  the  current,  shows  the  incorrectness  of  the  theory  put  forward  by  the  present 
author  (1904  Ji),  in  which  stimulation  was  supposed  to  be  due  to  the  variations  in  pressure 
produced  through  the  varied  movements  of  the  animal  in  its  spiral  course. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


75 


Certain  authors  (Dale,  1901,  Statkewitsch,  1903  a)  have  reported  that 
Paramecia  sometimes  swim  with  the  current.  But  in  these  cases  ir- 
regular currents  have  been  used,  such  as  are  produced  by  stirring  the 
water  containing  the  animals.  Using  a  tube,  the  present  author  has 
found  the  results  to  be  practically  uniform,  the  animals  swimming  up 
stream.  If  the  reverse  reaction  actually  occurs  at  times,  it  must  be  due 
to  some  change  of  internal  condition,  such  as  results  in  swimming  back- 
ward under  certain  circumstances ;  the  direction  of  the  current  over  the 
body  would  be  the  same  in  the  two  cases. 

If  the  explanation  of  the  reaction  to  water  currents  above  given  is 
correct,  this  reaction  is  clearly  analogous  to  the  compensatory  move- 
ments of  higher  animals,  as  Lyon  (1904)  has  brought  out  for  other 
organisms.  It  is  a  response  to  unusual  relations  with  the  environment, 
and  tends  to  restore  the  usual  relations. 


B.    Reactions  to  Gravity 

In  the  reaction  to  gravity  the  animals  place  themselves  with  anterior 
end  directed  upward,  and  as  a  result  swim  to  the  top  of  the  vessel  con- 
taining them,  forming  a  collection  there  (Fig.  56).  If  the 
tube  is  inverted  after  the  collection  is  formed,  so  that  the 
infusoria  are  now  at  the  bottom,  they  again  direct  the  ante- 
rior end  upward,  and  swim  to  the  top.  These  results  follow 
in  the  same  way  whether  the  upper  end  of  the  tube  is  open 
or    closed,    and    they    take  place   equally  well  when    the 

temperature  is  kept  uniform 
by  immersing  the    tube  in 

— 3C    runnin§  water. 

To  determine  the  way 
in  which  the  reaction  oc- 
curs, it  is  necessary  to  direct 
the  lenses  of  a  microscope 
of  long  focus  upon  a  region 
where  the  animals  are  tak- 
ing up  the  position  with  long 
axis  in  the  direction  of 
gravity. 


KU 


Fig.  57. — Tube  used  in  observing 
the  way  in  which  Paramecium  reacts  to 
gravity. 


Fig.   56.  — 
Paramecia   col- 

This  may  best  be  lected  at  the  top 
accomplished  by  placing  the  ° 


tube,  after  Jen- 

animals  in  a  U-shaped  tube,  sen  (1893). 
at  first  with  the  free  ends  upward.     After  the  animals  have  become 
grouped  at  the  two  free  ends,   the  tube  is  inverted   (Fig.   57).     The 
Paramecia  now   move   upward,  reach  the  cross-piece  of  the   U,    and 


76  BEHAVIOR   OF   THE   LOWER    ORGANISMS 

move  across  it  to  the  opposite  side.  Reaching  this,  they  at  first  con- 
tinue the  course  by  swimming  obliquely  downward,  to  the  point  x. 
Here  the  reaction  occurs;  the  animals  turn  around  and  swim  upward 
again.  Studying  the  movements  of  the  Paramecia  at  this  point,  one  ob- 
serves that  the  forward  motion  becomes  slower,  while  the  spiral  course 
becomes  wider.  The  animals  swerve  more  strongly  than  usual  toward 
the  aboral  side,  so  that  the  anterior  end  swings  about  in  a  circle,  as  in 
Figs.  37  and  38.  Thus  the  animals  are  giving  the  avoiding  reaction, 
"trying"  successively  many  different  positions.  This  is  continued  or 
repeated  till  after  a  time  they  come  into  a  position  with  anterior  end 
upward.  The  strong  swerving  then  ceases;  the  animals  swim  upward 
in  the  usual  spiral  course. 

The  position  of  individuals  at  rest  against  a  solid  is  usually  quite 
independent  of  gravity.  The  body  axis  may  be  placed  at  any  angle  with 
the  pull  of  gravity,  with  either  end  higher.  The  contact  reaction  inter- 
feres with  the  reaction  to  gravity,  preventing  it  almost  completely.  Yet 
there  is  a  tendency,  even  when  in  contact  with  a  solid,  to  take  a  position 
with  anterior  end  above.  If  Paramecia  are  placed  in  clean  water  in  a 
clean,  upright  glass  tube,  in  the  course  of  time  many  individuals  come  to 
rest  against  the  perpendicular  walls.  It  will  now  be  found,  in  some 
cases,  that  a  considerable  portion  of  the  animals,  though  by  no  means 
all,  are  resting  with  the  body  axis  nearly  in  line  with  gravity  and  with 
anterior  end  upward.  When  a  swimming  individual  places  itself  in  con- 
tact with  the  wall,  it  is  often  seen  to  make  a  sudden  turn  toward  the 
aboral  side,  just  as  it  comes  to  rest,  till  the  anterior  end  is  upward ;  then 
it  remains  in  that  position.  The  proportion  thus  oriented  with  reference 
to  gravity  is  in  some  cultures  sufficiently  great,  amounting  perhaps  to 
half  the  individuals,  to  show  that  the  position  is  not  accidental.  In 
other  cultures  there  may  be  almost  no  indication  of  any  influence  of 
gravity  on  the  position  of  the  attached  specimens. 

The  precise  nature  of  the  determining  factor  in  the  reaction  to  gravity 
is  very  obscure.  Jensen  (1893)  held  that  the  reaction  is  due  to  the  dif- 
ference in  pressure  between  the  upper  and  lower  portions  of  the  organism. 
The  cilia  on  the  side  where  the  pressure  was  greatest  (the  lower  side) 
were  supposed  to  beat  more  rapidly,  thus  turning  the  animal  directly 
upward.  But,  as  we  have  seen  above,  exact  observation  of  the  move- 
ments of  the  individuals  shows  that  the  reaction  does  not  take  place  in 
this  way.  Moreover,  the  difference  in  pressure  between  the  two  sides 
of  the  organism  is  in  certain  reacting  infusoria  only  one  millionth  of  the 
total  pressure,  and  this  difference  seems  beyond  question  too  slight  to 
act  as  an  effective  stimulus. 

Davenport  (1897,  p.  122)  held  that  the  reaction  to  gravity  is  due  to 


THE   BEHAVIOR   OF   INFUSORIA;  PARAMECIUM  77 

the  fact  that  the  resistance  in  moving  upward  is  greater  than  the  resist- 
ance in  moving  downward,  owing  to  the  fact  that  the  animal  is  heavier 
than  water.  To  the  changes  in  resistance  as  it  swims  up  or  down,  the 
animal  reacts.  This  view  was  accepted  and  elaborated  by  the  author 
of  the  present  work  (Jennings,  1904  h).  But  to  this  can  be  made  an 
objection  analogous  to  that  which  is  fatal  to  the  corresponding  view  for 
the  reaction  to  water  currents.  Under  the  uniform  action  of  gravity, 
as  Radl  (1903,  p.  139)  has  pointed  out,  it  is  not  apparent  how  any  such 
difference  of  resistance  could  be  perceived  by  the  organism.  The  ani- 
mal would,  with  the  same  action  of  the  cilia,  and  overcoming  the  same 
resistance,  move  somewhat  more  rapidly  downward  than  upward.  But 
it  is  very  questionable  if  this  slight  comparative  difference  in  rate  could 
be  perceived  by  the  organism, —  though  this  is  of  course  not  impossible. 
In  any  case,  the  fact  that  resting  individuals  may  react  to  gravity 
appears  fatal  to  the  view  at  present  under  consideration. 

The  view  having  the  greatest  probability  is  perhaps  that  suggested 
by  Lyon  (1905).  The  animal  contains  substances  of  differing  specific 
gravity;  this  Lyon  has  demonstrated.  The  distribution  of  these  sub- 
stances must  change  with  the  various  positions  taken  by  the  animal. 
When  the  anterior  end  is  directed  downward  the  redistribution  of  inter- 
nal substances  thus  induced  acts  as  a  stimulus,  causing  the  usual  re- 
action. The  animal  "tries"  new  positions  till  it  reaches  one  with 
anterior  end  upward;  then  the  reaction  ceases  and  the  animal  remains 
in  the  position  so  reached. 

Whatever  the  cause  for  the  reaction  to  gravity,  the  stimulation  it 
induces  is  evidently  very  slight,  and  its  effect  is  easily  annulled  by  the 
action  of  other  agents.  As  we  have  seen,  the  contact  reaction  usually 
prevents  the  reaction  to  gravity.  The  same  is  true  of  most  other  stimu- 
lating agents.  Almost  any  other  stimulus  that  may  be  present  produces 
its  usual  effect  without  interference  from  gravity,  so  that  the  reaction  to 
gravity  is  seen  clearly  only  in  the  absence  of  most  other  stimuli.  Thus, 
if  the  walls  of  the  vessel  containing  the  animals  are  not  clean,  or  if  the 
water  contains  many  solid  particles  in  suspension,  often  no  reaction  to 
gravity  can  be  observed. 

Furthermore,  the  reaction  to  gravity  becomes  reversed  under  cer- 
tain conditions.  Sometimes  nearly  all  the  individuals  in  a  given  cul- 
ture swim  downward  instead  of  upward.  This  result  may  be  produced 
in  cultures  having  originally  the  more  usual  upward  tendency,  in  a 
number  of  different  ways  (Sosnowski,  1899 ;  Moore,  1903).  These 
will  be  mentioned  in  our  section  on  reactions  to  two  or  more  stimuli. 


78  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

C.    Reaction  to  Centrifugal  Force 

Conditions  similar  to  those  due  to  gravity  may  be  produced  by  a 
centrifugal  force,  and  Paramecia  then  react,  as  might  be  expected,  in 
the  same  way  as  to  gravity.  Jensen  (1893)  shows  that  if  a  tube  contain- 
ing Paramecia  is  placed  in  a  horizontal  position  on  a  centrifuge  and 
whirled  at  a  certain  rate,  the  infusoria  tend  to  swim  toward  that 
end  of  the  tube  next  to  the  centre.  In  a  tube  12  cm.  long,  with  the 
inner  end  2  cm.  from  the  centre,  the  phenomena  were  well  shown 
when  the  tube  was  whirled  at  the  rate  of  four  turns  per  second,  for  ten  or 
fifteen  minutes.  In  such  a  tube  the  Paramecia  at  the  outer  end,  where 
the  movement  is  fastest,  are  carried  by  the  centrifugal  force,  against 
their  active  efforts,  to  the  outer  end  of  the  tube ;  this  is  of  course  a  purely 
passive  phenomenon.  The  remainder  of  the  Paramecia  swim  toward 
the  end  of  the  tube  next  the  centre  and  collect  there ;  this  is  the  active 
part  of  the  reaction. 

This  movement  toward  the  inner  end  of  the  tube  is  doubtless  due  to 
the  same  causes,  whatever  they  may  be,  that  produce  the  upward  move- 
ment in  the  reaction  to  gravity.  Lyon  (1905)  has  shown  that  the  body 
contains  substances  of  varying  specific  gravity,  some  of  which  collect, 
under  strong  centrifugation,  at  that  end  of  the  animal  which  is  at  the 
outer  end  of  the  tube.  This  redistribution  is  probably  the  cause  of  the 
reaction  to  centrifugal  force.  If  the  passage  of  such  substances  into 
the  anterior  end  should  act  as  a  stimulus  to  the  usual  reaction,  this 
would  produce  the  results  actually  observed. 

6.      RELATION    OF   THE    ORIENTATION    REACTIONS   TO    OTHER    REACTIONS 

We  are  now  in  a  position  to  define  the  difference  between  these  orien- 
tation reactions  and  the  others  that  we  have  described,  and  to  see  why 
the  result  of  the  avoiding  reaction  is  to  produce  a  certain  position  of 
the  body  axis  in  one  set  of  cases,  while  it  does  not  in  the  others. 

In  the  reactions  to  mechanical  stimuli,  chemicals,  osmotic  pressure, 
heat  and  cold,  and  powerful  light,  the  avoiding  reaction  is  caused  by  the 
transition  from  one  external  condition  to  another;  by  a  change  in  the 
intensity  of  action  of  some  agent, —  the  change  being  of  such  a  charac- 
ter as  to  lead  away  from  the  optimum.  As  a  result,  the  organism  tries 
repeated  different  directions  of  movement  (in  the  avoiding  reaction)  till 
it  hits  upon  one  in  which  the  transition  is  toward  the  optimum  instead 
of  away  from  it ;  in  this  direction  it  continues.  This  does  not  require 
the  body  axis  to  take  any  definite  orientation,  since  as  a  rule  there  are 
various  directions  in  which  the  animal  can  move  and  be  on  the  whole 
approaching  the  optimum.  Furthermore,  the  body  axis  might  be  in  any 
position,  provided  the  movement  were  on  the  whole  toward  the  optimum. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  79 

But  in  the  reactions  to  water  currents,  gravity  and  centrifugal  force, 
it  is  a  certain  position  of  the  body  that  results  in  stimulation ;  displace- 
ment of  the  cilia,  or  of  certain  internal  constituents,  occur  in  certain 
positions  of  the  body,  causing  disturbances  to  which  the  animal  reacts, 
as  usual,  by  the  avoiding  reaction.  This  reaction  consists  in  successively 
"trying,"  not  only  different  directions  of  locomotion,  but  also  different 
positions  of  the  body  axis,  as  a  glance  at  Figs.  37-39  will  show.  As  soon 
therefore  as  a  position  is  reached  in  which  the  disturbance  causing  the 
reaction  no  longer  exists,  the  reaction  of  course  stops ;  the  animal  there- 
fore retains  this  axial  position.1 

A  comparison  of  the  reactions  to  these  two  sets  of  agents  brings  out 
strongly  the  general  adaptiveness  and  effectiveness  of  the  reaction 
method  of  the  infusorian.  The  avoiding  reaction  is  of  such  a  charac- 
ter as  to  bring  about  in  a  systematic  way  (1)  different  directions  of 
movement;  (2)  different  axial  positions;  (3)  different  environmental 
conditions  (of  temperature,  chemicals,  etc.).  If  any  one  of  these  puts 
an  end  to  the  disturbance  which  caused  stimulation,  the  reaction  of 
course  stops  at  that  point,  and  the  animal  retains  the  direction  of  move- 
ment, axial  orientation,  or  environmental  condition  thus  reached.  If  a 
certain  axial  orientation  must  be  reached  before  the  stimulating  dis- 
turbance ceases,  then  the  result  of  the  reaction  will  be  to  produce  this 
orientation.  If  the  disturbance  ceases  before  a  common  orientation  of 
all  the  individuals  is  reached,  then  no  common  orientation  will  occur. 
In  other  words,  the  method  of  reaction  is  such  as  to  bring  about  any 
condition  whatsoever  that  is  required  in  order  to  put  an  end  to  stimula- 
tion, —  provided  of  course  that  this  condition  is  attainable.  It  will 
therefore  produce  in  some  cases  a  certain  direction  of  movement,  in  other 
cases  a  certain  axial  orientation,  in  other  cases  the  retention  of  a  certain 
environmental  condition,  just  as  circumstances  may  require. 

LITERATURE  IV 

A.  Reactions  to  contact  with  solids  :  Putter,  1900;  Jennings,  1897,  1899. 

B.  Reactions  to  chemicals  :  Jennings,  1897,  1899  c;   Greeley,  1904;  Barratt, 
1905. 

C.  Reactions  to  heat  and  cold :  Jennings,  1904;  Mendelssohn,  1895,  1902, 
1902  a,  1902  b. 

D.  Reactions  to  light :  Hertel,  1904. 

E.  Reactions  to  water  currents :  Jennings,  1904//:  Lyon,  1904,  1905. 

F.  Reactions  to  gravity  and  centrifugal  force :  Lyon,  1905  ;  Jensen,  1893  ;  Jen- 
nings, 1904//;  Sosnowski,  1899;  Moore,  1903. 

1  It  is  worthy  of  note  that  the  position  of  orientation  is  not  one  in  which  a  median 
plane  of  symmetry  takes  up  a  definite  position  with  reference  to  the  external  agent,  as  is 
sometimes  set  forth.  The  infusorian  when  oriented  continues  to  revolve  on  its  long  axis, 
so  that  no  more  can  be  maintained  than  that  the  longitudinal  axis  (in  reality  the  axis  of 
the  spiral  path)  is  in  line  with  the  orienting  force. 


CHAPTER  V 

BEHAVIOR   OF   PARAMECIUM    {Continued) 
Reactions  to  Electricity  and  Special  Reactions 


i.     reactions  to  electricity 

The  reactions  of  Paramecia  to  electricity  are  more  complex  than 
those  to  other  stimuli.  This  is  owing  to  certain  factors  peculiar  to  the 
action  of  the  electric  current,  which  interfere  with  the  usual  reaction 
method. 

The  gross  features  in  the  behavior  under  the  action  of  electricity  may 
be  seen  as  follows.  The  Paramecia  are  placed  in  a  watch-glass  or  other 
small  vessel,  and  through  the  water  containing  them  an  electric  current 
is  passed  (Fig.  58,  A).  Unpolarizable  electrodes  should  be  used,  though 
the  gross  features  in  the  reaction 
may  be  observed  with  platinum 
electrodes.  A  current  such  as  is 
produced  by  six  or  eight  chromic 
acid  cells  is  needed.  As  soon  as  the 
current  begins  to  pass,  all  the  Para- 
mecia swims  toward  the  cathode  or 


Fig.  58.  — A,  General  appearance  of  Paramecia  reacting  to  the  electric  current.  After 
Verworn  (1899).  The  current  is  passed  by  means  of  unpolarizable  brush  electrodes  through 
a  cell  with  porous  walls.  The  infusoria  have  gathered  at  the  cathodic  side.  B,  Magnified 
view  of  a  portion  of  the  swarm  as  it  moves  toward  the  cathode.      After  Verworn. 

negative  electrode.  The  swarm  of  infusoria  all  moving  in  the  same 
direction  present  a  most  striking  appearance  (Fig.  58,  B).  If  while 
all  are  swimming  toward  the  cathode  the  direction  of  the  current  is 
reversed,  the  Paramecia  at  once  turn  around    and    swim    toward   the 

80 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  8 1 

new  cathode.  If  the  electrodes  are  small  points,  the  Paramecia  swim 
in  curves,  such  as  are  known  to  be  formed  by  the  current  (Fig.  59). 
If  while  all  are  moving 
toward  the  cathode  the  cur- 
rent is  interrupted,  the  group 
breaks  up  and  the  Paramecia 
scatter  in  all  directions. 

If  the  current  is  at  first 
very  weak,  the  Paramecia  do 

ii  ,  r  Fig.  59. — A,  Curves  followed  by  Paramecia  when 

not  react  snarply,   only  a  ICW  pointed  electrodes  are  used.     B,  Collection  of  Para- 

of     them     swimmin0"     toward  mecia  behind    the  cathode,   when    the   electrodes  are 

the      cathode.  When     the  P^ed  close  together.     After  Verworn  (,899). 

strength  of  the  current  is  increased,  more  of  the  animals  react  and  the 
movement  is  more  rapid,  till  at  a  certain  strength  of  current  practically 
all  are  swimming  rapidly  to  the  cathode.  With  a  further  increase  in 
the  current,  the  rate  of  progression  toward  the  cathode  becomes  slower. 
As  the  increase  continues,  the  rate  of  swimming  decreases  till  progress 
nearly  or  quite  ceases.  The  animals  now  remain  in  position,  with 
anterior  ends  directed  toward  the  cathode,  but  not  moving  in  either 
direction.  Increasing  the  current  still  farther,  the  animals  begin  to 
swim  backward  toward  the  anode.  At  this  time  each  Paramecium 
is  seen  to  have  become  deformed,  being  short  and  thick.  If  the  cur- 
rent is  farther  increased,  the  animals  burst  at  one  end  and  go  to  pieces. 
These  remarkable  phenomena  were  first  observed  by  Verworn  (1889  a). 
How  is  this  striking  behavior  brought  about?  Why  do  the  Para- 
mecia first  all  go  to  the  cathode,  then  in  a  stronger  current  stop,  then 
swim  backward  to  the  anode  ? 

A.   Reaction  to  Induction  Shocks 

In  attempting  to  answer  these  questions,  it  will  be  best  to  take  up 
first  the  reactions  to  single  induction  shocks.  To  observe  the  reactions 
accurately,  the  Paramecia  must  be  placed  in  some  viscid  but  not  inju- 
rious substance,  such  as  the  jelly  produced  by  allowing  a  few  quince 
seeds  to  soak  in  a  watch-glass  of  water  containing  the  animals  (Statke- 
witsch,  1904  a).  This  makes  the  movements  so  slow  that  they  can  be 
followed  under  the  microscope.  The  reaction  to  induction  shocks  under 
these  conditions  has  been  studied  especially  by  Statkewitsch  (1903). 
When  an  induction  shock  is  passed  through  a  drop  of  such  fluid  con- 
taining Paramecia,  the  animals  are  found  to  react  especially  at  that 
part  of  the  body  which  is  next  the  anode.  Here  the  cilia  are  suddenly 
reversed,  striking  forward  instead  of  backward ;   the  ectosarc  contracts 


82 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


+ 


:<cr> 


sharply,  and  trichocysts  are  thrown  out  (Fig.  60).     If  the  current  is  a 
very  weak  one,  only  the  reversal  of  cilia  occurs ;  with  a  stronger  current 

the  other  phenomena 
appear.  With  a  very 
powerful  current, 
contraction  and  dis- 
charge of  trichocysts 
occur  also  at  the 
cathode,  and  with  a 
further  increase  of 
current,  over  the 
whole  body.  The 
animal  at  the  same 
time  becomes  de- 
formed and  usually 
goes  to  pieces. 

Fig.  60.  —  Effect  of  induction  shocks  on  Paramecia  in  different            x      .1  <r 

positions.     After  Statkewitsch    (1903).      Trichocysts    discharged,            -'■^   lli-Q  current  01 

cilia  reversed,  and  contraction  of  the  ectosarc,  at  the  anodic  side  moderate  Strength 

or  end,  in  a  moderate  current.  ,,  ,       r      ... 

the  reversal  of  cilia, 
beginning  at  the  anode,  quickly  spreads  over  the  entire  body,  causing 
the  animal  to  swim  backward.  This  movement  is  the  beginning  of 
the  avoiding  reaction.  After  swimming  backward  a  short  distance  the 
animal  turns  toward  the  aboral  side  and  swims  forward  in  a  new 
direction.  Thus  the  reaction  to  an  induction  shock  is  of  essentially  the 
same  character  as  the  reaction  to  other  strong  stimuli. 

Paramecium  reacts  to  induction  shocks  more  readily,  as  might  be 
expected,  when  the  sensitive  anterior  end  is  directed  toward  the  anode. 
When  in  this  position,  it  reacts  to  currents  that  are  too  weak  to  produce 
reaction  in  specimens  occupying  other  positions.  According  to  Roesle 
(1902),  Paramecium  reacts  more  readily  when  the  oral  surface  is  toward 
the  anode  than  when  in  other  positions,  indicating  that  the  region  about 
the  mouth  is  especially  sensitive.  While  this  seems  probable  on  general 
principles,  it  was  not  confirmed  by  the  thorough  work  of  Statkewitsch 
(1903).  In  some  cases  an  induction  shock,  like  a  weak  mechanical 
stimulus,  causes  in  place  of  the  avoiding  reaction  a  movement  forward 
(Roesle,  1902). 

Since  the  animal  is  most  stimulated  when  the  anterior  end  is  directed 
toward  the  anode,  and  this  stimulation  causes  as  a  rule  the  avoiding  re- 
action, one  would  expect  that  if  the  stimulation  came  repeatedly  from 
the  same  direction,  the  animal  would  after  a  time  reach  a  position  with 
anterior  end  directed  away  from  the  anode.  This  is  exactly  what  occurs. 
If  frequent  induction  shocks  are  passed  in  a  certain  direction  through 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  83 

the  water,  the  animals  all  become  pointed  toward  the  cathode  and  swim 
in  that  direction  (Birukoff,  1899,  Statkewitsch,  1903).  This  happens 
even  when  the  current  is  so  weak  that  a  single  induction  shock  causes 
no  reaction.  There  is  a  summation  of  the  effects  of  the  successive 
shocks  until  a  reaction  is  produced  (Statkewitsch,  1903).  As  most  com- 
monly used,  induction  currents  pass  alternately  in  opposite  directions. 
The  induced  current  in  one  direction  is  due  to  the  closing  of  the  circuit 
in  the  primary  coil,  while  the  immediately  following  current  induced  in 
the  opposite  direction  is  due  to  the  breaking  of  the  circuit  in  the  primary 
coil.  The  induced  currents  due  to  the  breaking  of  the  circuit  are,  as  is 
well  known,  more  powerful  than  those  produced  by  the  closing  of  the 
circuit.  When  both  currents  pass  through  the  preparation  alternately, 
Paramecia  react  primarily  to  the  stronger  "break"  currents.  They 
move  toward  the  cathode  of  these  stronger  currents  and  are  apparently 
not  affected  by  the  weaker  "make"  shocks  (Birukoff,  1899,  Statke- 
witsch, 1903  a). 

B.   Reaction  to  the  Constant  Current 

If  in  place  of  induction  shocks  a  continuous  electric  current  is  used, 
the  result  is  the  same  as  was  described  in  the  last  paragraph.  The 
Paramecia  place  themselves  with  anterior  end  directed  toward  the 
cathode  and  swim  in  that  direction  (Fig.  58). 

From  what  we  know  of  the  behavior  of  Paramecium  under  the  action 
of  other  stimuli,  we  might  suppose  that  the  whole  secret  of  this  behavior 
lies  in  the  production  of  the  avoiding  reaction  when  the  anterior  end  is 
directed  toward  the  anode.  This  reaction,  continuing  until  a  position 
was  reached  where  the  anterior  end  was  no  longer  stimulated,  would 
cause  it  to  become  directed  toward  the  cathode.  If  the  anode  stimula- 
tion still  continued,  now  at  the  posterior  end,  the  animal  would  continue  to 
swim  forward  toward  the  cathode,  for  to  stimulation  at  the  posterior  end, 
as  we  have  seen,  the  animal  responds  by  swimming  forward.  If  this  were 
the  method  of  reaction,  the  behavior  under  the  electric  current  would 
be  of  the  same  character  as  under  the  stimuli  which  the  animal  meets 
in  its  natural  existence. 

But  a  study  of  the  exact  movements  of  the  animals  shows  that  there 
is  present  another  factor  which  is  peculiar  to  the  action  of  the  electric 
current.  To  detect  this  the  precise  movements  of  the  cilia  under  the 
action  of  the  current  must  be  examined.  The  cilia  themselves  may  be 
directly  observed  in  specimens  placed  in  some  viscous  medium  (see 
Statkewitsch,  1904  a).  Or  the  effective  movements  of  the  cilia  may  be 
determined  by  mingling  with  the  fluid  containing  them  a  quantity  of 
finely  ground  India  ink.     By  its  aid  the  direction  of  the  currents  pro- 


84 


BEHAVIOR   OF    THE   LOWER    ORGANISMS 


duced  by  the  cilia  becomes  evident.1  In  this  way  we  find  that  it  is  not 
alone  at  the  anode  that  the  electric  current  is  active,  but  that  a  peculiar 
effect  is  produced  also  at  the  cathode.  Here  the  direction  of  the  cilia 
is  reversed  (Fig.  61)  so  that  they  point  forward,  and  their  effective  stroke 
is  forward,  tending  to  drive  the  animal  backward.     When  the  electric 

current  is  weak  and  the  animals  are  swim- 
ming toward  the  cathode,  the  cilia  are  re- 
versed only  at  the  anterior  end  (Fig.  61,  1), 
the  reversal  extending  a  little  farther  down 
on  the  oral  side  than  elsewhere.  At  the 
anterior  tip  the  water  currents  are  forward 
instead  of  backward  (Fig.  62,  a),  and  the 
cilia  themselves  are  clearly  seen  to  be 
pointed  forward  (Fig.  61,  1).  When  the 
animal  is  swimming  most  rapidly  toward  the 
cathode,  this  effect  is  very  slight ;  almost 
all  the  cilia  of  the  body  are  beating  back- 
ward in  the  usual  way. 

If    the    current   is   made  stronger,  this 
cathodic  effect  increases.     The  cilia  become 
Fig.  61.  — Progressive  cathodic  reversed  farther  and  farther  back,  till  with  a 

reversal  of  the  cilia  and  change  of  .  ^         r      ^  ^  •  ^ 

form  in  Paramecium  as  the  con-  certain  strength  of  the  electric  current  the 
stant    electric    current    is   made  cilia  on  the  anterior   half  of  the  body  are 

stronger.     The  cathode  is  supposed      .    .,  .  r  ,    ^,  ,,  .        .     , - 

to  he  at  the  upper  end.    The  cur-  striking  forward,  those  on  the  posterior  half 

rent  is  weakest  at  1,  where  only  a  backward  (Fig.  6l,  3).2  The  Water  Clir- 
few  cilia  are   reversed.      2-6,   Sue-  ,  ,  .  .... 

cessive   changes   as    the    current  is    rents    produced     are    111    Opposite  directions, 

gradually  increased.    After  Statke-  making  the   animal   the  centre  of  a  sort  of 

witsch  (1003  a).  ,       .         ,.  1      ,  .  ... 

cyclonic  disturbance  in  the  water,  which 
gives  a  most  extraordinary  appearance  (Fig.  62,  b).  The  two  sets  of 
cilia  oppose  each  other,  so  that  the  animal  seems  to  be  trying  to  swim 
in  two  opposite  directions  at  once.  Up  to  a  certain  strength  of  the  elec- 
tric current  the  posterior  cilia  prevail  over  the  anterior  ones,  so  that  the 
animal  swims  forward.  But  the  movement  becomes  slower  and  more 
labored  as  the  electric  current  is  increased,  until  in  time  the  two  sets  of 
cilia  balance  each  other.  Then  the  animal  remains  in  place,  revolving 
rapidly  on  its  long  axis,  or  it  shoots  first  a  short  distance  forward,  then 
a  little  backward.  With  a  still  further  increase  of  the  electric  current, 
the  cathodic  effect  increases  to  such  an  extent  that  the  reversed  cilia  gain 


1  The  Paramecia  must  be  in  a  thin  layer  of  fluid;  this  may  be  attained  by  supporting 
the  cover-glass  on  thin  sheets  of  filter  paper  and  introducing  the  current  through  this 
paper. 

2  This  peculiar  effect  was  first  observed  by  Ludloff  (1895). 


THE  BEHAVIOR   OF   INFUSORIA;   PARAMECIUM 


85 


the  upper  hand,  and  the  animal  swims  backward  toward  the  anode. 
The  cilia  are  now  reversed  even  behind  the  middle  (Fig.  61,  4,  5).  The 
body  is  deformed,  becoming  short  and  thick,  and  pinched  to  a  point  at 
the  anode  end,  while  the  cathode  end  is  swollen.  Finally  the  animal 
usually  bursts  and  goes  to 
pieces ;  before  this  happens 
almost  all  the  cilia  have 
become  reversed  (Fig. 
61,  6). 

When  a  Paramecium 
is  transverse  or  oblique  to 
the  direction  of  a  current 
at  the  time  the  circuit  is 
closed  (Fig.  63,  c,  e),  cer- 
tain striking  effects  are 
produced.     If  a  current  of 


medium  strength  is  em- 
ployed, such  as  causes  re- 
versal of  about  half  the 
cilia,  the  following  results 
are  observed.  On  the 
anode  side  the  cilia  strike 
backward,  as  usual.  On 
the  cathode  side  the  cilia 
strike  forward.  As  a  re- 
sult the  animal,  when  in  a 
transverse  position,  must 
turn  directly  toward  the 
cathode  side, 
both   sides   of    the    body 

tending  to  produce  this  effect,  as  indicated  by  the 
c  and  e.  This  happens  even  when  the  oral  side  is  directed  toward  the 
cathode  (Fig.  63,  e).  The  animal  then  turns  toward  the  oral  side,  — 
a  result  never  produced  by  other  stimuli,  and  due  to  the  peculiar 
cathodic  effect  of  the  current. 

This  tendency  to  turn  directly  toward  the  cathodic  side  is  compli- 
cated in  certain  positions  of  the  animal  by  the  usual  strong  tendency  to 
turn,  under  the  influence  of  stimuli,  toward  the  aboral  side,  —  that  is, 
to  respond  by  the  typical  avoiding  reaction.  If  the  anterior  end  is 
directed  toward  the  anode  at  the  time  the  circuit  is  closed,  the  animal  in- 
variably turns  toward  its  aboral  side,  the  cilia  taking  the  position  shown 
in  Fig.  63,  b.     This  method  of  turning  is  apparently  due  to  the  fact  that 


Fig.  62.  —  Water  currents  produced  by  the  cilia  in  the 

electric  current,      a,  Electric  currents  weak;   water  currents 

reversed  only  at  cathodic  tip.     b,  Electric  currents  stronger; 

the    cilia    of  water   currents  reversed   over  cathodic  half  as  far  back  as 

the  middle. 

arrows  in  Fig.  63, 


86 


BEHAVIOR   OF    THE   LOWER   ORGANISMS 


the  backward  stroke  of  the  oral  cilia  is  more  powerful  than  that  of  the 
opposing  aboral  cilia.  For  the  same  reason  the  animal  turns  toward 
the  aboral  side  even  when  in  the  position  shown  in  Fig.  63,  a,  where  it 
would  be  more  direct  to  turn  toward  the  oral  side.  Between  this  posi- 
tion (a)  and  the  transverse  position  with  oral  side  to  the  cathode  (e), 
there  is  a  position  in  which  the  tendencies  to  turn  in  opposite  directions 
are  exactly  balanced  (/).  The  animal  tries,  as  it  were,  to  turn  in  opposite 
directions  at  the  same  time,  so  that  it  remains  in  position,  though  the 


(/- 


Fig.  63.  —  Effects  of  the  electric  current  on  the  cilia  of  Paramecia,  and  direction  of  turning 
in  different  positions.  The  oral  side  is  marked  by  an  oblique  line.  The  large  arrows  show 
the  direction  toward  which  the  animal  turns.  The  small  internal  arrows  indicate  the  direction 
in  which  the  cilia  of  the  corresponding  quarter  of  the  body  tend  to  turn  the  animal.  In  all 
positions  save  c  and  e  the  cilia  of  different  regions  oppose  each  other.  From  a  to  d  the  turning 
is  toward  the  aboral  side;  from  d  to  /,  toward  the  oral  side.  At  /  the  impulse  to  turn  is  equal  in 
both  directions,  and  there  is  no  result  till  by  revolution  on  the  long  axis  the  animal  comes  into 
a  position  with  aboral  side  to  the  cathode. 

cilia  are  beating  violently,  causing  complicated  currents  in  the  water. 
This  independent  and  opposing  activity  of  the  cilia  of  different  parts  of 
the  body  is  characteristic  of  the  effects  of  the  electric  current,  and  is  not 
found  in  the  reactions  to  other  stimuli.  In  the  position  shown  in  Fig. 
63,  /,  the  revolution  on  the  long  axis,  which  is  a  part  of  the  normal 
motion  of  the  animal,  soon  interchanges  the  position  of  oral  and  aboral 
sides,  whereupon  the  infusorian  of  course  turns  at  once  towards  the 
aboral  side,  till  its  anterior  end  is  directed  toward  the  cathode. 

Thus  in  a  considerable  preponderance  of  all  possible  cases  the  ani- 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  87 

mal  turns  toward  the  aboral  side,  as  it  does  under  other  stimuli.  But 
in  certain  positions  (from  d  to  /,  Fig.  63)  it  turns  directly  toward  the  oral 
side,  a  result  not  producible  by  other  stimuli. 

If  the  direction  of  the  electric  current  is  frequently  reversed,  certain 
peculiar  effects  are  produced.  If  the  reversal  occurs  at  the  moment 
when  the  anterior  end  has  become  directed  toward  the  cathode,  then  the 
animal  continues  to  turn  toward  the  aboral  side  till  the  anterior  end  is 
pointed  toward  the  new  cathode.  By  repeated  properly  timed  rever- 
sals, the  animals  can  be  caused  to  spin  round  and  round,  —  always 
toward  the  aboral  side.1  If  the  intervals  between  the  reversals  of  the 
current  are  made  less,  so  that  the  animal  has  not  yet  become  pointed 
toward  the  cathode,  it  swings  back  over  the  space  through  which  it  has 
turned.  Thus  the  animals  may  be  made  to  swing  back  and  forth  or  turn 
round  and  round,  remaining  in  the  same  spot,  like  animated  galva- 
nometers, —  the  anterior  end  pointing  out  the  direction  of  the  current. 

If  the  rate  of  reversal  is  much  increased,2  so  that  the  animals  have 
scarcely  time  to  begin  swinging  in  a  certain  direction  before  a  new  re- 
versal occurs,  then  certain  other  phenomena  result;  these  have  been 
described  by  Statkewitsch  (1903,  1903  a).  The  Paramecia  which  are 
swimming  toward  one  electrode  when  the  current  is  closed  usually  con- 
tinue to  swim  in  the  same  direction  for  a  time,  as  if  reacting  to  only  one 
of  the  current  directions.  Those  not  already  pointed  toward  one  of  the 
electrodes  usually  take  quickly  the  transverse  position.  Thus,  soon  after 
the  beginning  of  the  experiment,  part  of  the  animals  are  swimming 
toward  the  electrode  at  the  right,  part  toward  that  at  the  left,  while  the 
rest  are  transverse.  Soon  those  not  transverse  have  reached  the  region 
of  the  electrode  toward  which  they  are  swimming.  Thus  the  Paramecia 
are  now  divided  into  three  groups,  —  a  group  at  the  right  swimming 
toward  the  right  electrode,  another  at  the  left  swimming  towards  the 
left  electrode,  and  a  central  group  swimming  athwart  the  current  (Fig. 
64).  After  a  time  the  transverse  position  is  assumed  also  by  those 
directed  toward  the  electrodes,  especially  if  the  current  is  made  stronger 
or  the  rate  of  reversal  is  increased.  Thus  at  a  later  stage  all  or  nearly 
all  are  transverse;  they  swim  across  the  current,  some  toward  one  side 
of  the  preparation,  some  toward  the  other. 

The  reason  for  taking  the  transverse  position  when  the  current  is 
rapidly  reversed  seems  to  be  as  follows:    We  have  seen  above  that  to 

1  As  soon  as  a  specimen  has  made  a  half  revolution  on  its  long  axis,  as  may  happen,  it 
of  course  seems  to  spin  in  the  opposite  direction,  because  the  aboral  side  has  taken  up  a 
new  position. 

2  The  strength  of  the  current  remaining  the  same  in  both  directions,  not  varying  as  in 
ordinary  induction  shocks. 


88 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


^\1 


•-'.."   .■.-.""  '  '  '.'.    /:y./:.... .  " 


single  electric  shocks  the  animals  react  more  strongly  when  the  anterior 
end  is  directed  toward  the  anode.  Often  there  is  no  reaction  when  they 
are  in  the  opposite  position.  Consider  a  specimen  that  is  oblique,  as  in 
Fig.  63,  b'.   The  current  comes  alternately  from  the  right  and  left.    To 

the  current  coming  from  the  left 
(anode  at  the  left)  the  Paramecium 
reacts  strongly,  since  its  anterior  end 
is  directed  toward  the  anode.  It 
therefore  turns  its  anterior  end  in  the 
opposite  direction,  —  to  the  right. 
To  the  opposite  current,  on  the  other 
hand,  it  reacts  little  or  not  at  all, 
since  the  anterior  end  is  not  directed 
JL         \^^^V\^ViU^f^£        toward    the    anode.     Continuing   thus 

to  react  to  the  repeated  currents  from 
the  left,  it  must  come  into  the  trans- 
verse position.  Here  the  anterior  end 
has  the  same  relation  to  both  currents ; 
hence  it  swings  as  far  to  one  side  as  to 
the  other.  Since  it  changes  its  posi- 
tion very  little  at  any  one  reversal,  it 
maintains  on  the  whole  the  transverse 


'SI 


• •■,,•,..■■„-, 


w:::.--:-1-'  '."•  -•'_"  ~-*\ 


WHMW 


yt£0zv4##j&&&^j&^?~,* 


position. 
Under 


a   constant   current 
the    general    effect 


in 
of 


one 
the 


Fig.  64.  —  Positions  taken    by    Para 
mecia  in  rapidly  reversed  currents,    a,  Posi 
tions   in   \veak    currents,    or    in    moderate  direction 
currents  at  the  beginning  of  the  experiment. 

c  and  d,  Positions  taken  in  stronger  cur-  behavior  is  of  course  to  cause  the  am- 

rents,  or  after  the  experiment  has  lasted  for  mals  j-q  pass  t0  the  cathode.     Here  they 
some  time.     After  Statkevvitsch  (1903  a).  ,  .  .  -n  t 

may  gather  in  a  dense  mass.  But  it 
the  cathode  is  so  placed  that  the  Paramecia  can  pass  behind  it,  they  do 
this,  thus  reaching  a  region  where  the  current  is  not  acting  (Fig.  59, 
B).  Here  they  swim  about  in  all  directions.  If  one  comes  by  chance 
again  into  the  field  of  the  current,  it  is  at  once  returned,  by  the  usual 
reaction,  to  the  region  behind  the  cathode.  If  in  any  other  way  certain 
areas  are  left  free  from  the  action  of  -the  current  or  with  very  little  cur- 
rent, the  animals  gather  in  these  free  areas.  Birukoff  (1899)  has  de- 
scribed and  figured  many  such  cases,  produced  under  induction  shocks 
by  the  aid  of  electrodes  of  different  forms ;  his  results  have  been  extended 
by  Statkewitsch  (1903  a). 

It  is  evident  that  the  reaction  to  the  electric  current  differs  funda- 
mentally from  the  known  behavior  under  other  classes  of  stimuli.  Under 
other  stimuli  the  movements  are  coordinated,  all  tending  toward  the  same 
end,  while  in  the  electric  current  different  parts  of  the  body  oppose  each 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  89 

other.  The  behavior  thus  becomes  uncoordinated,  lacking  unity.  The 
animal  seems  to  strive  to  perform  two  opposite  actions  at  once.  The 
anterior  cilia  drive  the  animal  backward,  the  posterior  cilia  forward.  In 
certain  positions  (Fig.  63,  /)  part  of  the  cilia  tend  to  turn  the  animal  to 
the  right,  others  to  the  left.  The  action  of  the  current  is  more  local  and 
direct  than  that  of  other  stimuli,  producing  opposed  reactions  in  dif- 
ferent parts  of  the  body.  The  whole  secret  of  this  extraordinary  be- 
havior lies  in  the  cathodic  reversal  of  the  cilia.  If  this  cathodic  effect 
were  non-existent,  the  behavior  under  the  action  of  the  electric  current 
would  probably  be  the  same  as  under  other  stimuli.  The  reaction  due 
to  the  anodic  stimulation  is,  as  we  have  seen,  the  same  as  that  due  to 
other  strong  stimuli,  and  in  the  constant  current  the  anodic  cilia  strike 
backward  in  the  usual  way.  If  the  anodic  stimulation  alone  existed, 
the  animal  would  doubtless  become  directed  to  the  cathode  by  the  method 
of  trial  and  would  swim  in  that  direction.  But  as  the  behavior  actually 
occurs,  there  is  nothing  like  a  trial  of  different  positions.  The  cathodic 
reversal  of  the  cilia  forces  the  animal  directly  into  a  certain  orientation. 
The  reaction  is  not  due,  like  that  to  chemicals,  to  the  change  in  condi- 
tions as  the  animal  passes  from  one  region  to  another.  It  is  not  due  to 
a  tendency  to  collect  about  the  cathode,  for,  as  we  have  seen,  if  it  is 
possible,  the  animals  go  beyond  the  cathode.  Moreover,  in  a  strong 
current  there  is  no  movement  to  the  cathode,  and  in  a  still  stronger 
current  the  movement  is  away  from  the  cathode,  though  the  orientation 
remains  the  same  in  both  cases.  All  these  peculiarities  in  the  behavior 
are  due  to  the  cathodic  reversal  of  the  cilia. 

What  is  the  cause  of  this  fundamental  feature  of  the  reaction  to  the 
electric  current,  —  the  cathodic  reversal?  Many  theories  have  been 
proposed  to  account  for  the  reaction  to  electricity,  though  often  these 
do  not  touch  this  fundamental  feature  in  any  way.  It  will  be  better  to 
reserve  an  account  of  these  theories  until  we  have  examined  the  behavior 
of  other  infusoria  under  the  action  of  electricity  (see  Chapter  IX). 

2.  OTHER  METHODS  OF  REACTION  IN  PARAMECIUM 

In  Paramecium  there  are  certain  methods  of  reacting  to  stimuli  which 
we  have  not  yet  described.  These  are,  first,  local  contractions  of  the 
ectosarc,  and  second,  discharge  of  trichocysts.  Neither  of  these  seem  to 
play  any  important  part  in  regulating  the  relation  of  the  organism  to 
the  surrounding  conditions. 

Slight  local  contractions  of  the  ectosarc  occur  in  response  to  many 
stimuli.  Since  the  ectosarc  of  Paramecium  is  not  known  to  contain  con- 
tractile elements,  the  way  in  which  these  are  brought  about  is  unknown. 


9° 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


A  discharge  of  trichocysts  is  produced  by  many  different  agents. 
The  trichocysts  are  rodlike  sacs  in  the  ectosarc,  perpendicular  to  the 
outer  surface.  Their  contents  are  ejected,  under  certain  conditions,  into 
the  water,  forming  long  threads.  According  to  some  authors,  these 
threads  have  a  definite  structure,  and  are  probably  preformed  within 
the  animal.  Others  suppose  the  threads  to  be  formed  by  the  coagula- 
tion of  a  fluid  contained  within  the  sacs.  After  discharge  of  the  tricho- 
cysts the  animal  appears  to  be  surrounded  by  a  zone  of  radiating  fibres 
(Fig.  65). 

The  discharge  of  trichocysts  under  the  influence  of  stimuli  has  been 
studied  especially  by  Massart  (1901  a),  and  by  Statkewitsch   (1903). 

Crushing  the  animal  causes 
discharge  of  trichocysts  in 
the  region  injured.  Weaker 
mechanical  stimuli  do  not 
have  this  effect.  If  the  ani- 
mal is  heated  rapidly  till  it 
is  killed,  it  discharges  the 
trichocysts   before  dying;   if 

Fig.  65. —  Paramecium  with  trichocysts  discharged,  heated  slowly,  this  effect  is 
as  a  result  of  the  application  of  picric  acid.  ^  producecL      Neither   Cold 

nor  increased  osmotic  pressure  have  any  effect  on  the  trichocysts.  Many 
chemicals  produce  the  discharge,  particularly  various  acids.  Saturated 
solution  of  picric  acid  causes  a  sudden  discharge  of  all  the  trichocysts  at 
once.  One-fourth  per  cent  methylene  blue  produces  a  slow  and  irregular 
discharge  successively  from  different  parts  of  the  body.1  If  any  agent 
acts  on  a  limited  portion  of  the  body  surface,  the  trichocysts  of  only  that 
region  are  discharged.  Many  chemicals  kill  the  animal  without  dis- 
charge of  the  trichocysts. 

A  weak  induction  shock  causes  discharge  of  the  trichocysts  at  the 
anode  only  (Fig.  60);  a  stronger  shock  causes  discharge  at  both  anode 
and  cathode.  A  still  stronger  shock  causes  discharge  of  the  trichocysts 
over  the  entire  surface  of  the  body  (Statkewitsch,  1903). 

In  the  discharge  of  the  trichocysts  we  have  a  phenomenon  compara- 
ble to  the  definite  reflex  actions  observed  in  various  organs  of  higher 
animals.  The  function  of  the  trichocysts  is  uncertain.  They  are  usu- 
ally supposed  to  be  weapons  of  defence.  If  the  Paramecium  is  seized 
by  an  animal  which  is  attempting  to  prey  upon  it,  the  trichocysts  will  of 
course  be  discharged  from  the  injured  region.     But  whether  they  really 

1  To  demonstrate  the  discharge  of  the  trichocysts  it  is  convenient  to  use  picric  acid 
alone  or  picric  acid  to  which  a  little  aniline  blue  has  been  added.  In  the  latter  case  the 
trichocysts  become  colored  blue  (Massart). 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  91 

serve  for  defence  seems  questionable.  Certainly  the  infusorian  Didi- 
nium  (Fig.  113),  which  is  the  chief  enemy  of  Paramecium,  is  not  hindered 
in  the  least  from  seizing  and  devouring  the  animal  by  the  discharge  of 
trichocysts.  It  is  possible  that  the  discharge  is  really  an  expression  of 
injury,  —  a  purely  secondary,  even  pathological,  phenomenon,  like  the 
formation  of  vesicles  on  the  surface  of  an  injured  specimen. 

LITERATURE  V 

A.  Reaction  of  Paramecium  to  electricity:  Verworn,  1889  a  ;  Ludloff,  1895  ; 

BlRUKOFF,    1899,     I904;     ROESLE,     I902  ;     PUTTER,    I900;      STATKEWITSCH,      I903, 

1903  a,  1904;  Jennings,  1904  h\  Bancroft,  1905;  Coehn  and  Barratt,  1905. 

B.  Discharge  of  trichocysts  as  a  reaction  :  Massart,  1901  a. 


CHAPTER  VI 

BEHAVIOR   OF   PARAMECIUM   {Continued) 

Behavior  under  Two  or  More  Stimuli  ;  Variability  of  Be- 
havior ;  Fission  and  Conjugation  ;  Daily  Life  ;  General 
Features  of  the  Behavior 

i.   behavior  under  two  or  more  stimuli 

The  behavior  thus  far  described  is  that  which  takes  place  under  the 
influence  of  but  a  single  kind  of  stimulation.  But  normally  the  condi- 
tions are  as  a  rule  more  complex  than  this ;  the  animal  is  affected  by 
several  sets  of  stimuli  at  once.  What  is  the  behavior  under  such  condi- 
tions ?  If,  while  the  Paramecium  is  reacting  to  the  stimulus  a,  the  stim- 
ulus b  acts  upon  it,  will  it  react  in  the  usual  way  to  b  ?  Or  will  it  con- 
tinue to  react  to  a?  Or  will  its  action  form  a  compromise  between  the 
usual  reactions  to  the  two  agents?  Or  will  it,  finally,  react  in  a  new 
way,  different  from  the  usual  reactions  to  either  a  or  b  ? 

Let  us  examine  first  the  behavior  under  the  simultaneous  action  of 
the  contact  stimulus  and  of  other  usual  stimuli.  As  we  have  seen,  the 
contact  stimulus  often  causes  the  animal  to  come  to  rest  and  behave  in 
a  characteristic  manner,  while  other  classes  of  stimuli  usually  induce 
the  avoiding  reaction  or  a  movement  forward.  Thus  opposite  reactions 
are  induced  by  the  two  kinds  of  stimuli  acting  separately.  What  will  be 
the  result  when  the  two  act  together? 

If  the  animal  is  at  rest  against  a  mass  of  vegetable  matter  or  a  bit  of 
paper  under  the  action  of  the  contact  stimulus,  and  it  is  then  struck 
with  the  tip  of  a  glass  rod,  we  find  that  at  first  it  may  not  react  to  the 
latter  stimulus  at  all.  A  touch  that  would  cause  a  free  swimming  speci- 
men to  give  the  avoiding  reaction  in  a  pronounced  way  often  has  no  evi- 
dent effect  on  the  quiet  specimen.  Sometimes,  however,  a  touch  coming 
from  behind  causes  the  animal  to  move  forward,  still  remaining  in  con- 
tact with  the  solid  object ;  it  thus  creeps  a  short  distance  over  the  sur- 
face of  the  solid.  Finally,  a  strong  blow  on  the  anterior  end  causes  the 
animal  to  leave  the  solid  and  give  the  typical  avoiding  reaction. 

Thus  we  find  that  under  the  simultaneous  action  of  the  two  stimuli 

92 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  93 

the  infusorian  may  either  react  to  the  more  effective  of  the  two,  which- 
ever it  is,  without  regard  to  the  other,  or  its  behavior  may  be  a  sort  of 
compromise  between  the  usual  results  of  both. 

If  specimens  showing  the  contact  reaction  are  heated,  it  is  found  that 
they  do  not  react  to  the  heat  until  a  higher  temperature  has  been  reached 
than  that  necessary  to  cause  a  definite  reaction  in  free  swimming  speci- 
mens. Thus  Putter  (1900)  found  that  at  30  degrees  C.  all  the 
free  specimens  are  strongly  affected,  moving  about  rapidly  in  all  direc- 
tions, while  the  attached  specimens  remain  quiet  or  make  only  slight 
vibratory  movements.  Many  of  them  remain  attached  until  the  tem- 
perature has  reached  37  degrees,  when  the  free  specimens  are  dashing 
about  wildly.  At  this  temperature  or  a  somewhat  lower  one  the  at- 
tached specimens  become  free ;  they  then  dash  about  as  furiously  as  the 
others.  Thus  the  contact  reaction  interferes  with  the  reaction  to  heat, 
preventing  it  until  a  much  higher  temperature  has  been  reached  than  is 
necessary  to  cause  reaction  in  free  specimens. 

On  the  other  hand,  both  heat  and  cold  interfere  with  this  contact 
reaction.  Paramecia  much  above  or  much  below  the  usual  tempera- 
ture do  not  settle  against  solids  with  which  they  come  in  contact,  but 
respond  instead  by  a  pronounced  avoiding  reaction.  At  a  still  higher 
temperature  even  the  avoiding  reaction  ceases.  A  Paramecium  coming 
against  a  solid  presses  the  anterior  end  against  it  and  continues  to  try  to 
swim  forward,  —  succeeding  only  in  revolving  on  its  long  axis  (Massart, 
1901  a). 

Specimens  in  contact  with  a  solid  react  less  readily  to  chemicals  than 
do  free  specimens,  so  that  a  higher  concentration  is  required  to  indue  ■ 
the  avoiding  reaction.  On  the  other  hand, 
immersion  in  strong  chemicals  prevents 
the  positive  contact  reaction ;  Paramecia 
under  such  conditions  coming  against  a 
solid  react  by  the  avoiding  reaction.  In 
this  case,  then,  the  effect  of  the  chemical 

is    tO    change    the    method    of    reacting    to  Fig.  66.  —  Paramecia  which  have 

another    Stimulus  —  tO    the     Solid    object,   formed  a  ring  about  a  bubble  of  co2, 
l-ii  1  and  have  then  come  to  rest  against  the 

Certain  other  chemicals  have  the  oppo-  g\ass  supporting  rods,  forming  two 
site  effect,  favoring  the  positive  contact  dense  groups. 
reaction.  This  is  notably  true  of  carbon  dioxide.  In  water  contain- 
ing  this  substance  the  infusoria  are  strongly  inclined  to  settle  down 
against  any  object  with  which  they  may  come  in  contact.  They  thus 
often  form  under  these  conditions  dense  masses  attached  to  the  glass 
rods  used  for  holding  up  the  cover-glass  (Fig.  66),  though  usually  they 
do  not  come  to  rest  against  smooth,  hard  objects. 


94  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

The  contact  reaction  may  completely  prevent  the  reaction  to  gravity. 
Paramecia  placed  in  a  tube  which  contains  many  bits  of  solid  matter,  or 
has  its  walls  rough  or  dirty,  usually  do  not  rise  to  the  top,  but  settle 
against  the  solid  matter  on  the  wall  and  remain.  They  may  thus  re- 
main scattered  through  all  parts  of  the  tube,  or  may  gather  in  any  por- 
tion of  it  where  the  material  inducing  the  reaction  is  found.  Specimens 
at  rest  against  a  solid  may  occupy  any  position  with  reference  to  gravity. 
In  similar  ways  the  contact  reaction  may  prevent  the  usual  reaction 
to  water  currents. 

The  interference  between  the  contact  reaction  and  the  reaction  to 
the  electric  current  produces  a  number  of  peculiar  results.  If  a  weak 
electric  current  is  passed  through  a  preparation  containing  many  speci- 
mens attached  to  a  bit  of  debris  or  to  the  surface  of  the  glass,  the  free 
specimens  swim  at  once  toward  the  cathode,  while  the  attached  speci- 
mens do  not  react  at  all.  If  the  current  is  made  stronger,  it  produces 
for  an  instant  the  usual  effect  on  the  cilia  of  the  attached  specimens. 
The  cathodic  cilia  strike  forward,  the  anodic  cilia  backward.  But  this 
does  not  continue;  after  a  moment  the  contact  reaction  resumes  its 
sway,  and  the  cilia  have  their  usual  positions.  If  the  current  continues, 
after  a  short  time  the  cilia  are  again  affected  as  before;  then  resume 
their  original  positions.  This  may  occur  many  times,  —  the  two  stimuli 
alternating  in  their  control  of  the  cilia.  If  the  current  is  made  much 
stronger,  the  animal  finally  leaves  the  solid.  It  then  swims  directly 
to  the  cathode  in  the  usual  way.  To  induce  this  reaction  in  a  resting 
specimen,  it  requires  as  a  rule  two  or  three  times  as  intense  a  current  as 
that  needed  for  producing  the  same  effect  on  free  swimming  animals. 

If  the  electric  stimulus  is  first  in  action  and  the  Paramecium  then 
comes  in  contact  with  a  solid,  somewhat  different  results  are  produced. 
If  the  current  is  weak,  often  the  animal,  swimming  toward  the  cathode, 
ceases  to  react  to  the  electricity  on  coming  against  the  solid ;  it  may 
then  take  up  any  position  on  the  surface  of  the  solid.  If  it  comes  against 
the  surface  film  of  the  water,  or  the  surface  of  the  glass  slide,  it  may 
cease  its  forward  movement  only  for  an  instant,  then,  becoming  free,  it 
may  swim  again  toward  the  cathode.  If  the  current  is  a  little  stronger 
(such  as  to  produce  the  maximum  rapidity  of  movement  toward  the 
cathode,  in  free  swimming  specimens),  a  different  effect  is  produced. 
The  Paramecium  stops  against  the  surface  of  the  solid,  and  places  itself 
transversely  or  obliquely  to  the  current,  with  the  oral  surface  toward  the 
cathode  (Fig.  67).  Here  it  remains,  the  current  produced  by  the  cilia 
being  everywhere  backward  save  in  the  oral  groove,  where  it  is  forward. 
If  the  electric  current  is  reversed,  the  oral  cilia  strike  strongly  backward, 
and   the   animal  at   once  turns  on  its  short  axis  till  the  oral  surface 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  95 

faces  the  new  cathode.  It  remains  in  this  position  till  the  current  is 
reversed  anew.  Thus,  when  in  contact  with  a  surface,  Paramecia  often 
show  a  transverse  orientation  with  reference  to  the  electric  current.  At 
times  the  animal  while  in  this  position  moves  forward  along  the  surface 
with  which  it  is  in  contact,  transversely  to  the  current;  on  reversal  of 
the  current  it  turns  about  and  moves  in  the  opposite  direction.  This 
may  often  be  observed  if  the  Paramecia  are 
placed  on  a  slide  in  a  thin  layer  of  water 
through  which  the  electric  current  is  passed. 
Many  of  them  in  swimming  come  against  1 
the  glass  or  the  surface  film  of  the  water. 
Thereupon  they  begin  to  move  transversely 
to  the  current,  as  just  described.  Mean- 
while the  free  swimming  specimens  con- 
tinue to  pass  toward  the  cathode. 

1  .,,_..  Fig.     67.  —  Oblique     position 

With  a   Stronger   current   a  Still    different  taken  by  Paramecium  in  contact  with 

effect    is   produced.      The    Paramecia    are  a  surface,  when  under  the  action  of 

1  -ii  tne  eiectnc  current. 

swimming   forward   in    the   slow,   cramped 

manner  that  is  characteristic  for  strong  currents.  On  coming  in  conT 
tact  with  the  surface  film  or  the  glass,  the  animals  at  once  begin  to 
move  backward  (toward  the  anode)  instead  of  forward.  This  con- 
tinues as  long  as  the  contact  continues.  On  becoming  free  they  swim 
forward  again.  The  reason  for  this  behavior  seems  to  be  as  follows : 
In  a  strong  electric  current,  as  we  know,  the  anterior  cilia  tend  to  drive 
the  animal  backward,  the  posterior  cilia  forward  (Fig.  62,  b) ;  the  latter 
prevail.  The  contact  reaction,  as  we  have  seen,  causes  the  cilia  behind 
the  region  of  contact  to  cease  movement.  When  swimming  forward 
under  the  conditions  mentioned,  the  Paramecia  usually  come  in  con- 
tact with  the  surface  at  the  thickest  part  of  the  body,  near  the  middle 
of  its  length.  Thereupon,  owing  to  the  contact  reaction,  the  cilia  be- 
hind this  spot,  driving  the  animal  forward,  cease  to  beat,  while  the  cilia 
in  front,  driving  it  backward,  continue  their  action.  Hence,  the 
anterior  cilia  gain  the  upper  hand  and  force  the  animal  backward. 

Why  does  this  contact  stimulus  thus  interfere  with  the  reaction  to 
other  stimuli?  There  are  two  possible  factors  to  be  considered  here, 
one  physical,  the  other  physiological.  The  animal  seems  actually  to 
attach  itself  to  solids,  probably  by  a  secretion  of  mucus.  Such  a  secre- 
tion is  very  evident  in  many  infusoria,  though  it  has  not  been  demon- 
strated in  Paramecium.  This  attachment  would,  in  a  purely  physical 
way,  impede  the  movements  due  to  other  stimuli.  While  it  is  possible 
that  this  factor  may  play  a  small  part  in  the  matter,  it  is  clear  that  it  is 
not  the  important  or  essential  factor.     If  it  were,  we  should  see  the  cilia 


q6  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

of  the  attached  animal  move  in  the  usual  manner  under  the  influence  of 
stimuli,  though  these  movements  would  not  have  the  usual  effect.  As  a 
matter  of  fact,  in  most  cases  we  see  nothing  of  the  kind.  The  cilia 
either  do  not  move  at  all,  or  move  in  a  manner  different  from  that  occur- 
ring in  free  specimens.  The  essential  factor  in  the  interference  is  a 
physiological  one.  When  reacting  to  the  contact  stimulus,  the  animal 
is  less  easily  affected  by  other  stimuli,  and  when  reacting  to  the  other 
stimuli,  it  is  less  easily  affected  by  the  contact  stimulus.  Since  the  two 
stimuli  in  question  require  behavior  of  opposite  character,  it  is  indeed 
inevitable  that  one  should  give  away  to  the  other,  or  at  least  modify  the 
behavior  toward  it ;  both  cannot  receive  the  usual  reaction. 

Combinations  of  other  stimuli  have  been  less  investigated  than  those 
just  considered.  In  any  combination  the  reaction  to  gravity  gives  way, 
as  we  have  seen,  to  the  reaction  due  to  other  factors.  Paramecia  swim- 
ming upward  react  to  other  stimuli  without  hindrance,  and  Paramecia  at 
rest  against  a  surface  often  show  no  orientation  with  reference  to  gravity. 
The  reactions  to  chemical  and  electrical  stimuli  completely  supplant 
the  reactions  to  gravity.  In  a  vertical  tube  Paramecia  may  form  col- 
lections in  any  region  that  becomes  impregnated  with  carbon  dioxide  or 
may  avoid  any  region  which  contains  a  repellent  chemical.  If  an  elec- 
tric current  is  passed  through  a  vertical  tube,  the  Paramecia  react  to  it 
in  exactly  the  same  manner  as  under  other  conditions,  swimming  toward 
the  cathode  whether  this  is  above  or  below.  Sosnowski  (1899)  and 
Moore  (1903)  have  shown  that  many  different  stimuli  modify  the  reac- 
tion to  gravity,  changing  the  direction  in  which  the  animals  swim.  If 
Paramecia  in  the  culture  fluid  swim  upward,  mixture  with  tap  water,  or 
with  chemicals  of  various  sorts,  often  causes  them  to  swim  downward. 
This  effect  soon  disappears,  however,  and  the  animals  return  to  the  top. 
Increase  of  temperature  to  30  degrees  (Sosnowski),  or  decrease  to  2  de- 
grees (Moore),  often  has  the  same  temporary  effect.  The  same  result 
is  at  times  produced  by  shaking  or  jarring  the  tube  containing  the  ani- 
mals ;  they  go  to  the  bottom,  returning  in  a  short  time  to  the  top.  The 
effect  of  all  these  agents  varies  with  different  cultures  of  Paramecia ;  in 
some  cultures  the  reaction  to  gravity  is  easily  changed,  in  others  with 
difficulty  or  not  at  all. 

Reactions  to  chemicals  often  interfere  with  the  reaction  to  the 
electric  current.  If  through  a  preparation  of  Paramecia  that  are 
gathered  in  an  area  containing  carbon  dioxide,  as  in  Fig.  68,  A,  an 
electric  current  is  passed,  the  animals  swim  to  the  cathode  side  of  the 
area,  then  stop.  All  gather  in  this  region,  seeming  to  make  vain  efforts 
to  cross  the  invisible  boundary  (Fig.  68,  B).     Observation  of  individuals 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


97 


shows  that  as  soon  as  they  reach  the  boundary  of  the  area  of  carbon 
dioxide,  they  give  the  avoiding  reaction,  in  the  usual  way,  and  pass  back 
into  the  area.  Here  they  become  oriented  again  by  the  electric  current, 
and  pass  again  to  the  boundary,  where  they  react  as  before.  Thus  the 
reaction  to  the  electric  current  prevails  until  a  region  of  a  sudden  change 
in  chemical  character  is  reached;  the  reaction  to  this  then  supplants 
the  reaction  to  the  current.  If  the  current  is  reversed,  the  animals 
gather  in  the  same  way  at  the  opposite  side  of  the  area  of  carbon  dioxide 
(Fig.  68,  C).     If  the  current  is  made  very  powerful  and  is  long  continued, 


B        - 


Fig.  68.  —  Interference  of  chemicals  with  the  reaction  to  the  electric  current.  At  A  Para- 
mecia  have  gathered  in  an  area  containing  C02.  At  B  an  electric  current  is  passed  through 
the  preparation  with  cathode  at  the  left;  the  animals  gather  at  the  left  edge  of  the  area  of  C02- 
At  C  the  current  has  been  reversed;  the  animals  are  therefore  gathered  at  the  right  edge  of  the 
area. 

the  Paramecia  are  one  by  one  caused  to  cross  the  boundary  of  the  acid 
area  and  to  swim  to  the  cathode.  If  a  drop  of  some  repellent  chemical 
—  as  sodium  chloride  or  an  alkali  —  is  introduced  into  a  preparation 
(Fig.  41),  the  Paramecia  of  course  leave  this  vacant.  If  the  electric 
current  is  passed  through  the  preparation,  the  Paramecia  swim  toward 
the  cathode;  coming  to  the  boundary  of  the  drop,  they  swim  around  it, 
leaving  it  empty,  and  thus  reach  the  cathode.  In  this  case  the  path 
followed  is  a  resultant  of  the  operation  of  the  two  stimuli,  —  the  orienta- 
tion due  to  the  electric  current  and  the  avoiding  reaction  produced  by 
the  chemical. 

If  the  entire  region  next  the  cathode  is  occupied  by  a  repellent  chemi- 
cal, the  Paramecia  may  be  forced  by  a  strong  and  long-continued  cur- 
rent to  enter  it  till  they  are  destroyed. 

A  very  peculiar  interaction  of  chemicals  and  the  electric  current  is 
seen  when  Paramecia  are  placed  in  physiological  salt  solution  (0.7  per 


98  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

cent)  and  the  current  is  passed  through  the  vessel.  The  strong  chemical 
causes  the  animals  to  swim  backward ;  the  current  orients  them  in  the 
usual  way;  the  result  is  that  they  swim  backward  to  the  anode.  This 
phenomenon  is  to  be  observed  in  solutions  of  various  chemicals,  as 
acids,  potassium  iodide,  sodium  carbonate,  etc.  It  will  probably  be 
found  to  occur  in  any  solution  that  causes  the  animals  to  swim  back- 
ward for  a  considerable  time.  It  should  be  investigated  further.  As 
soon  as  the  Paramecia  have  become  accustomed  to  the  chemical,  so  that 
they  no  longer  swim  backward  within  it,  they  react  to  the  current  in  the 
usual  way,  swimming  to  the  cathode. 

Thus  we  find  that  under  the  action  of  more  than  one  stimulus  Para- 
mecium may  behave  in  any  of  the  ways  which  we  mentioned  in  our 
first  paragraph  as  conceivable.  It  may  react  to  the  first  stimulus  with- 
out regard  to  the  second,  or  to  the  second  without  regard  to  the  first, 
depending  on  which  is  the  more  effective.  Such  results  are  often  pro- 
duced when  both  the  stimuli  are  sufficiently  strong  to  cause  reaction  if 
acting  alone.  Which  stimulus  shall  produce  its  characteristic  effect  some- 
times depends  on  which  comes  into  action  first.  Thus,  Paramecia  in 
contact  may  not  react  to  the  electric  current  or  to  heat;  while  free 
Paramecia  subjected  to  the  same  strength  of  current  or  degree  of  heat 
do  not  show  the  positive  contact  reaction.  This  condition  of  affairs 
seems  to  occur  throughout  the  animal  series;  in  higher  animals  we 
express  the  same  phenomenon  subjectively  by  saying  that  attention  to 
one  thing  prevents  attending  to  others. 

In  some  cases  the  behavior  shown  is  a  resultant  of  the  action  of  the 
two  stimuli.  Examples  of  this  are  seen  in  the  movement  along  a  surface 
under  the  simultaneous  action  of  the  contact  reaction  and  a  mechanical 
shock,  or  in  swimming  around  a  chemical  in  solution,  under  the  influence 
of  the  electric  current ;  or  in  swimming  backward  to  the  anode  when  in 
solutions  of  strong  chemicals. 

Finally,  the  effect  of  one  stimulus  is  sometimes  merely  to  change 
the  method  of  reaction  to  another.  Thus  heat  and  strong  chemicals 
cause  the  animal  to  respond  to  contact  by  the  avoiding  reaction  in  place 
of  the  positive  contact  reaction ;  carbon  dioxide  has  the  contrary  effect. 
The  modifications  of  the  reaction  to  gravity  above  mentioned  are  ex- 
amples of  the  same  thing.  Cases  of  this  character  have  much  theoret- 
ical interest.  We  shall  return  to  them  in  considering  the  variability 
and  modifiability  of  the  reactions  of  Paramecium. 

2.     VARIABILITY    AND    MODIFIABILITY    OF   REACTIONS 

We  have  seen  in  the  last  section  that  the  behavior  of  Paramecium 
under  a  given  stimulus  may  be  determined  by  the  simultaneous  presence 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  99 

of  other  stimuli.  The  behavior  depends  not  only  on  the  stimulus  to 
which  it  is  primarily  reacting,  but  also  upon  other  external  conditions. 
May  the  nature  of  the  behavior  also  depend  upon  internal  conditions? 
In  other  words,  may  the  same  animal  under  the  same  external  conditions 
behave  differently  at  different  times?  May  Paramecium,  like  higher 
animals,  become  modified  by  the  stimuli  which  it  has  received,  or  by 
its  own  reactions,  so  as  to  react  for  the  future  in  a  manner  different  from 
its  reactions  in  the  past? 

It  is  difficult  to  obtain  evidence  on  this  question  for  Paramecium, 
because  the  animal  moves  about  so  rapidly  that  it  is  hardly  possible  to 
follow  a  given  individual  and  determine  whether  its  reactions  do  or  do 
not  change.  Much  more  is  known  in  regard  to  this  matter,  as  we  shall 
see  later,  for  the  fixed  infusorian  Stentor.  But  a  number  of  significant 
facts  have  been  brought  out  for  Paramecium. 

First  we  have  the  fact  that  the  presence  of  a  certain  agent  or  condi- 
tion may  alter   the   method    of   reaction    to    another.      Paramecia  in 
heated  water  react  to  solids  by  the  avoiding  reaction  in  place  of  the 
positive  contact  reaction;    Paramecia  in  a  solution  of  carbon  dioxide, 
on  the  other  hand,  are  much  more  likely  to  respond  by  the  positive 
contact  reactions.     Many  conditions  —  heat,  cold,  chemicals,  mechani- 
cal shock,  etc.  —  alter,  as  we  have  seen,  the  reaction  to  gravity,  causing 
the  animals  to  swim  downward  instead  of  upward.     Such  phenomena 
indicate  that  the  first  agents  alter  in  some  way  the  physiological  con- 
dition of  the  animals,  so  that  they  now  react  to  the  second  agent  in  a 
changed   manner.     This   conclusion   is   impressed   upon    the   observer 
by  the   behavior  of  the  organisms.     Specimens  in   heated   water  are 
swimming  about  violently,  so  that  we  should  not  expect  them  to  come 
to  rest  against  solids.     Those  in  carbon  dioxide  move  slowly  and  seem 
in  a  condition  predisposing  to  repose,  so  that  coming  to  rest  against 
solids  is   the '  reaction   that  might   be    anticipated.     The    interference 
between  the  two  stimuli  is  not  purely  physical.     There  is  nothing  in  the 
physical  action  of  heat  or  a  mechanical  jar  to  make  the  animals  move 
downward,  as  happens  when  the  agents  reverse  the  action  to  gravity. 
Indeed,  in  the  latter  case  one  can  plainly  see  that  the  downward  move- 
ment is  an  active  one.     The  only  explanation  possible  for  such  cases 
is  that  the  animals  have  become  changed  in  some  way  by  the  first  stimu- 
lus, so  that  they  now  react  in  an  altered  manner  to  the  second  stimulus. 
Further  we  find  that  there  are  great  differences  in  the  reactions  of 
different   individual    Paramecia,    and    especially   of    Paramecia    from 
different  cultures.     In  studying  the  reactions  to  chemicals,  one  often 
finds  that  a  few  individuals  swim  directly  into  the  given  solution,  while 
the  majority  give  the  avoiding  reaction  on  coming  in  contact  with  it, 


ioo  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

and  hence  remain  outside  (Jennings,  1899  c,  p.  373).  While  in  a  cer- 
tain case  individuals  from  one  culture  were  repelled  by^g-  per  cent  lithium 
chloride,  those  from  another  culture  were  found  to  be  quite  indifferent 
to  a  solution  of  the  same  chemical  sixteen  times  as  strong,  swimming 
readily  into  a  drop  of  J-  per  cent  lithium  chloride  (Jennings,  1899  c, 
p.  374).  When  placed  in  a  vertical  tube,  Paramecia  from  certain  cul- 
tures gather  at  the  top;  from  other  cultures  at  the  bottom;  while  in 
other  cases  they  remain  scattered  throughout  the  tube  (Sosnowski, 
1899).  Corresponding  variations  are  found  in  the  reaction  to  water 
currents.  Similar  differences  are  to  be  observed  with  regard  to  the 
positive  contact  reaction  (Putter,  1900,  p.  253).  Infusoria  in  certain 
cultures  are  strongly  inclined  to  attach  themselves  to  solids,  forming 
dense  masses  on  the  surface;  in  other  cultures  such  masses  are  never 
formed.  In  fresh  cultures  the  animals  are  usually  much  inclined  to 
attach  themselves  in  this  way ;  in  old  cultures  they  are  not.  Even  in 
a  culture  where  most  of  the  animals  attach  themselves,  there  are  always 
a  number  of  specimens  which  remain  persistently  free.  Variations  are 
to  be  observed  at  times  in  the  reactions  to  electricity  (Jennings,  1904  h). 
One  sometimes  observes  that  while  most  of  the  specimens  in  a  prepara- 
tion are  reacting  to  the  electric  current  in  a  precise  way,  a  few  speci- 
mens do  not  react  at  all,  swimming  about  at  random.  Sometimes 
single  specimens  will  be  seen  swimming  toward  the  anode,  while  all  the 
rest  swim  toward  the  cathode.  This  is  most  often  observed  after  the 
current  has  been  reversed  several  times. 

Whether  the  variations  mentioned  in  the  last  paragraph  are  due  to 
changes  which  have  occurred  during  the  life-time  of  the  animals,  or 
whether  they  are  permanent  differences  between  different  individuals 
we  do  not  know.  In  either  case  they  are  of  importance,  since  they  give 
much  opportunity  for  the  action  of  natural  selection.  This  is  a  point 
to  which  we  shall  return  later. 

We  know,  however,  that  sometimes  the  behavior  of  the  same  indi- 
vidual varies,  and  in  some  cases  we  can  form  an  idea  of  the  nature  of 
the  change  which  has  occurred.  If  a  Paramecium  is  subjected  to  a 
strong  induction  shock,  it  fails  for  some  time  thereafter  to  react  to  weak 
shocks,  though  at  the  beginning  it  reacted  to  these  (Statkewitsch,  1903). 
This  result  is  probably  due  to  a  change  in  the  animal  such  as  we  com- 
monly call  fatigue.  To  be  explained  possibly  in  a  similar  way  is  the 
following  occasional  observation.  A  specimen  in  the  continuous  elec- 
tric current  is  swimming  toward  the  cathode ;  on  reversal  of  the  current 
it  retains  its  orientation  and  continues  to  swim  forward,  —  now  of 
course  toward  the  anode.     This  lasts  usually  but  a  short  time. 

Paramecia  which  have  been  living  at  the  usual  temperatures  show 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  ioi 

a  temperature  optimum  of  about  24  to  28  degrees ;  if  they  are  kept  for 
some  hours  at  a  temperature  from  36  to  38  degrees,  the  optimum  rises 
to  30  or  32  degrees  (Mendelssohn,  1902).  A  change  in  the  individuals 
induced  in  this  way  is  commonly  spoken  of  as  acclimatization.  Simi- 
lar changes  could  doubtless  be  induced  in  the  reactions  to  chemicals 
and  to  other  stimuli ;   this  has  not  yet  been  done. 

Paramecia  that  have  long  been  deprived  of  food  behave  in  a  some- 
what different  manner  from  normal  individuals  (Moore,  1903;  Wal- 
lengren,  1902  a).  But  the  changes  in  behavior  are  apparently  due  to 
actual  structural  changes  in  the  organism,  due  to  lack  of  food,  and  render- 
ing it  impossible  for  the  animal  to  move  so  strongly  and  rapidly  (Wal- 
lengren,  1902  a).  Paramecia  kept  in  distilled  water  are  found  to  be 
much  more  sensitive  to  most  stimuli  than  usual  (Jennings,  1897;  Wal- 
lengren,  1902  a) ;  owing  apparently  to  lack  of  sodium  salts  in  the  body. 
This  condition  may  perhaps  be  called  that  of  salt  hunger.  If  a  small 
quantity  of  some  sodium  salt  is  added  to  the  distilled  water,  the  Para- 
mecia return  to  the  usual  condition  (Wallengren,  1902  a). 

Certain  changes  in  the  behavior  of  individuals  can  hardly  be  classi- 
fied as  due  either  to  fatigue,  acclimatization,  or  hunger.  If  a  bit  of 
filter  paper  is  placed  in  a  preparation  of  Paramecia,  the  following  be- 
havior may  often  be  observed.  An  individual  swims  against  it,  gives 
the  avoiding  reaction  in  a  slightly  marked  way,  swimming  backward 
a  little;  then  it  swims  forward  again,  jerks  back  a  shorter  distance, 
then  settles  against  the  paper  and  remains.  After  remaining  a  few 
seconds,  it  may  move  to  another  position,  still  remaining  in  contact 
with  the  paper.  Then  it  may  leave  the  paper  and  go  on  its  way.  All 
this  may  happen  without  the  slightest  evident  change  in  the  outer  con- 
ditions. So  far  as  can  be  seen,  the  Paramecium  first  responds  to  the 
solid  by  the  avoiding  reaction,  later  by  the  positive  contact  reaction, 
and  still  later  suspends  the  contact  reaction,  all  without  any  change  in 
external  conditions.  The  changes  inducing  the  change  in  reaction  must 
then  be  within  the  animal. 

Again,  as  we  have  seen,  jarring  Paramecia  which  have  collected  at 
the  top  of  a  tube  often  causes  them  to  swim  to  the  bottom  of  the  tube 
(Sosnowski,  Moore).  The  jarring  itself  lasts  but  a  moment,  while 
the  Paramecia  continue  for  some  time  after  to  swim  downward.  The 
shock  must  therefore  have  changed  the  physiological  condition  of  the 
animals,  so  that  they  now  show  a  change  of  reaction  to  gravity,  or 
possibly  a  lack  of  reaction  to  gravity.1 

1  It  is  possible  that  the  shock  merely  causes  them  to  swim  rapidly  in  any  direction 
that  is  open  to  them.  Since  they  are  already  at  the  top  of  the  tube,  the  only  direc- 
tion open  to  them  is  that  leading  downward. 


102 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


All  together,  it  is  clear  that  there  are  differences  in  behavior  due  to 
differences  in  the  internal  or  physiological  condition  of  the  animal,  — 
differences  shown  even  in  a  single  individual  at  different  times.  Some 
of  the  different  physiological  conditions  may  be  characterized  as  fatigue, 
as  acclimatization,  as  hunger,  or  the  like.  In  other  cases  they  cannot 
be  definitely  characterized.  We  clearly  have  slight  beginnings  of  the 
modification  of  behavior  through  the  previous  experiences  of  the  organism. 
The  analysis  of  this  matter  will  be  carried  farther  for  the  behavior  of 
unicellular  organisms  in  the  account  of  Stentor  (Chapter  X). 


3.     BEHAVIOR   IN   FISSION   AND   CONJUGATION 

At  intervals  certain  extraordinary  episodes  connected  with  the  pro- 
cesses of  reproduction  interrupt  the  usual  life  of  Paramecium.  The 
behavior  at  such  times  seems  not  to  differ  in  any  notable  manner  from 
the  usual  behavior.     We  shall  therefore  describe  it  only  briefly. 

Fission.  —  At  times  the  animal  begins  to  divide  into  two  by  a  trans- 
verse constriction  at  about  the  middle.  During  the  early  stages  of  the 
process  the  two  halves  act  in  unison.  The  currents 
of  water  are  driven  by  the  cilia  in  the  same  direction 
over  both,  and  the  two  halves  react  to  any  stimulus 
as  a  single  animal.  If  subjected  to  induction  shocks 
the  half  at  the  anode  responds  by  contraction  of  the 
ectosarc  and  discharge  of  trichocysts,  while  the 
cathode  half  does  not.  As  the  constriction  sepa- 
rating the  two  halves  becomes  very  deep,  so  that  they 
are  connected  only  by  a  slender  strand,  they  begin 
to  behave  more  independently.  The  anterior  half 
at  times  changes  its  direction  of  movement,  while  the 
posterior  half  tries  to  continue  straight  forward.  The 
connecting  strand  is  strained  and  bent  or  twisted. 
Soon  it  breaks,  and  the  two  individuals  are  separated. 

Conjugation.  —  In  conjugation  two  individuals  become  united  by 
their  oral  surfaces  (Fig.  69),  and  a  complicated  process  of  interchange 
of  nuclei  occurs.  The  union  of  two  specimens  seems  brought  about 
chiefly  by  the  usual  movements  and  reactions  of  the  animals,  taken  in 
connection  with  a  physical  change  of  the  body  substance  in  the  region 
of  the  oral  groove.  Here  the  surface  becomes  viscid,  so  that  if  another 
Paramecium  comes  in  contact  with  this  region,  the  two  stick  together. 
Often  two  individuals  may  be  seen  at  rest  close  together  on  the  surface 
of  a  bit  of  bacterial  zooglcea.  One  drags  its  posterior  end  across  the 
oral  groove  of  the  other,  whereupon  the  two  stick  together  (Fig.  70,  a). 


Fig.  60.  —  A  pair 
of  conjugating  Para- 
mecia. 


THE   BEHAVIOR   OF  INFUSORIA;  PARAMECIUM 


103 


Each  tries  to  continue  its  course,  so  that  they  pull  in  opposite  directions. 
One  may  drag  the  other  along  with  it,  or  the  two  may  finally  pull  apart. 
There  is  of  course  a  tendency  for  objects  to  be  brought  against  the 
oral  groove,  owing  to  the  strong  current  of  water  that  passes  along  this 
region ;  it  is  through  this  fact  that  Paramecium  gets  its  food  (compare 
Fig.  46).  This  tendency  operates  on  other  Paramecia  in  the  neigh- 
borhood as  well  as  on  inanimate  objects.  If  two  Paramecia  are  close 
together  with  oral  grooves  facing  each  other  (Fig.  71),  this  tendency  is 
reciprocal;   each  tends  to  draw  the  other  to  its  own  oral  surface.     On 


Fig.  70.  —  Groups  of  individuals  adhering  to  each  other  by  their  oral  surfaces,  from  cultures 
of  Paramecia  undergoing  conjugation,  a.  Two  attached  individuals  swimming  in  opposite 
directions,  b,  Three  individuals  attached  by  their  oral  surfaces  to  a  fourth,  c.  Three  indi- 
viduals irregularly  attached,  d,  A  conjugating  pair,  swimming  to  the  left,  with  a  third  individual 
attached  by  its  oral  surface  to  the  posterior  part  of  one  of  these,  and  a  fourth  individual  trans- 
versely attached  to  the  third.     The  third  and  fourth  were  dragged  about  by  the  first  pair. 

the  other  hand,  if  the  aboral  surfaces  face  each  other,  the  currents  tend 
to  separate  the  two  Paramecia.  Hence  when  two  Paramecia  come  in 
contact  it  will  usually  be  by  the  oral  surfaces.  This  often  happens  under 
usual  conditions,  but  no  conjugation  results,  because  the  oral  surfaces 
have  no  tendency  to  adhere ;  the  animals  therefore  quickly  separate 
again.  But  at  times  when  the  oral  surfaces  are  viscid,  specimens  which 
come  thus  in  contact  remain  united.  The  succeeding  internal  processes 
fall  in  the  field  of  physiology  rather  than  that  of  behavior.  Details 
concerning  them  will  be  found  in  text-books  of  zoology. 

Thus  nothing  seems  to  be  required  for  producing  conjugation  be- 
yond the  usual  movements  and  the  viscidity  of  the  oral  region.      The 


104 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


present  author  has  been  unable,  after  careful  study,  to  detect  any  differ- 
ences in  the  methods  of  reacting  during  periods  of  conjugation.  The 
groups  formed  on  the  surface  of  solids  and  the  rapid  movements  of  the 
organisms,  described  by  Balbiani  (1861,  p.  441),  as  occurring  at  such 

periods,  are  by  no  means  peculiar  to  conjugat- 
/   /  ing  infusoria.     They  take   place   in    the   same 
Sf%    /      manner  in  cultures  where  none  are  conjugating. 
The  significant  part  played  in  conjugation  by 
the  viscidity  of   the   oral    surfaces   is    demon- 
strated by  the    peculiar   phenomena   observed 
when   specimens  accidentally  come  in    contact 
irregularly.     This  often  happens  where  the  ani- 
mals are  numerous.     If  any  part  of  the  body  of 
one  specimen  comes  by  chance  against  the  oral 
surface  of  another,  the  two  stick  together,  with- 
out regard  to  their  relative  position. 

Often  groups  of  three  or  four  or  more  are 

tie  71. —  Currents  urging  .  . 

two  Paramecia  together  when  formed  in  this  way  (Fig.  70).     The  individuals 

the  oral  sides  face  one  another.  occupy  all   sorts  of  irregUlar  positions,  and  each 

endeavors  to  swim  forward  in  his  own  direction.  Some  are  pulled  back- 
ward, others  sidewise,  against  their  vigorous  struggles.  Often  one  suc- 
ceeds in  freeing  itself,  and  then  swims  away;  others  remain  caught  in 
such  groups  indefinitely.  Even  moribund  specimens  and  specimens 
undergoing  fission  sometimes  thus  become  united  irregularly  with 
others.  But  the  regular  union  of  individuals  by  the  oral  surfaces  is 
more  common  than  the  formation  of  irregular  groups,  owing  to  the 
strong  tendency,  produced  by  the  usual  currents,  for  Paramecia  to  come 
together  at  the  oral  surfaces. 

During  conjugation  the  two  united  individuals  behave  in  much 
the  same  way  as  a  single  specimen.  They  revolve  on  the  long  axis  to 
the  left  as  they  swim  through  the  water,  and  they  react  to  stimuli  by  the 
avoiding  reaction  in  the  usual  way.  The  direction  of  turning  in  the 
avoiding  reaction  seems  determined  usually  by  one  of  the  components; 
the  pair  always  turn  toward  the  aboral  side  of  this  particular  individual. 
If  subjected  in  the  transverse  position  to  an  induction  shock,  only  the 
specimen  next  the  anode  responds  by  ejecting  trichocysts  (Statkewitsch, 

I9°3)- 

4.     THE   DAILY   LIFE   OF   PARAMECIUM 

Let  us  now  try  to  form  a  picture  of  the  behavior  of  Paramecium  in 
its  daily  life  under  natural  conditions.  An  individual  is  swimming 
freely  in  a  pool,  parallel  with  the  surface  and  some  distance  below  it. 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  105 

No  other  stimulus  acting,  it  begins  to  respond  to  the  changes  in  distri- 
bution of  its  internal  contents  due  to  the  fact  that  it  is  not  in  line  with 
gravity.  It  tries  various  new  positions  until  its  anterior  end  is  directed 
upward,  and  continues  in  that  direction.  It  thus  reaches  the  surface 
film.  To  this  it  responds  by  the  avoiding  reaction,  finding  a  new  posi- 
tion and  swimming  along  near  the  surface  of  the  water.  Now  there 
is  a  strong  mechanical  jar,  —  some  one  throws  a  stone  into  the  water, 
perhaps.  The  Paramecium  starts  back,  tries  certain  new  directions, 
and  finishes  by  reacting  to  gravity  in  the  reverse  way  from  its  former 
reaction;  it  now  swims  downward.  But  this  soon  brings  it  into  water 
that  is  notably  lacking  in  oxygen.  To  this  change  it  responds  as  be- 
fore, trying  new  directions  till  it  has  come  near  the  surface  again.  Swim- 
ming forward  here,  it  approaches  a  region  where  the  sun  has  been 
shining  strongly  into  the  pool,  heating  the  water.  The  Paramecium 
receives  some  of  this  heated  water  in  the  current  passing  from  the 
anterior  end  down  the  oral  groove.  Thereupon  it  pauses,  swings  its  an- 
terior end  about  in  a  circle,  and  finding  that  the  water  coming  from  one 
of  the  directions  thus  tried  is  not  heated,  it  proceeds  forward  in  that 
direction.  This  course  leads  it  perhaps  into  the  region  of  a  fresh  plant 
stem  which  has  lately  been  crushed  and  has  fallen  into  the  water.  The 
plant  juice,  oozing  out,  alters  markedly  the  chemical  constitution  of 
the  water.  The  Paramecium  soon  receives  some  of  this  altered  water 
in  its  ciliary  current.  Again  it  pauses,  or  if  the  chemical  was  strong, 
swims  backward  a  distance.  Then  it  again  swings  the  anterior  end 
around  in  a  circle  (Fig.  38)  till  it  finds  a  direction  from  which  it  receives 
no  more  of  this  chemical;   in  this  direction  it  swims  forward. 

Thus  the  animal  swims  about,  continually  hesitating  as  it  reaches 
regions  where  the  conditions  differ,  trying  new  directions,  and  changing 
its  course  frequently.  Every  faint  influence  in  the  water  affects  it, 
for  the  animal  is  very  sensitive.  Other  Paramecia  swim  about  in  the 
same  way.  They  do  not  avoid  each  other,  but  often  strike  together; 
then  one  or  both  draw  back  and  turn  in  another  direction.  The  animal 
may  strike  in  the  same  way  against  stones  or  the  sides  of  a  glass  vessel. 
In  such  cases  it  may  be  compelled  to  try  successively  many  different 
directions  before  it  succeeds  in  avoiding  the  obstacle,  —  acting  like  a 
blind  man  who  finds  a  stone  wall  in  his  course. 

After  a  time  our  animal  comes  against  a  decayed,  softened  leaf. 
At  first  it  draws  back  slightly,  then  starts  forward  again,  and  places 
itself  against  the  leaf.  The  body  cilia  cease  their  action,  while  the  oral 
cilia  carry  a  strong  stream  of  water  to  the  mouth.  It  so  happens  that 
this  leaf  has  lately  fallen  into  the  water  and  has  no  bacteria  upon  it,  so 
that  the  Paramecium  receives  no  food.     Nevertheless  the  animal  "tries" 


106  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

it  for  a  while.  Other  Paramecia  may  gather  in  the  same  way,  but  after 
a  considerable  time  they  one  by  one  leave  the  dead  leaf.  Our  Para- 
mecium swims  about  again,  being  directed  hither  and  thither  by  the 
various  changes  in  the  chemical  constitution  or  temperature  of  the  water, 
till  it  comes  to  a  region  containing  more  carbon  dioxide  in  solution  than 
usual.  It  gives  no  sign  of  perceiving  this,  save  perhaps  by  swimming 
a  little  less  energetically  than  before.  The  area  containing  carbon 
dioxide  is  small,  and  soon  the  animal  comes  to  its  outer  boundary, 
where  the  water  drawn  to  its  oral  groove  contains  no  carbon  dioxide. 
It  stops,  and  tries  different  regions,  by  swinging  its  anterior  end  around 
in  a  circle,  till  it  again  finds  a  direction  from  which  it  receives  carbonic 
acid ;  in  that  direction  it  swims  forward.  Since  it  behaves  in  the  same 
way  whenever  it  comes  to  the  outer  boundary  of  the  carbonic  acid,  it 
remains  swimming  back  and  forth  within  this  region,  and  thus  in  time 
explores  it  very  thoroughly.  Finally  it  comes  upon  the  source  of  the 
carbon  dioxide,  —  a  large  mass  of  bacteria,  embedded  in  zooglcea,  that 
are  giving  off  this  substance.  The  infusorian  places  itself  against  the 
mass  of  zooglcea,  suspends  the  activity  of  the  body  cilia,  and  brings  a 
strong  current  of  water  along  the  oral  groove  to  the  mouth.  This  current 
removes  some  of  the  bacteria  from  the  zooglcea  and  carries  them  to  the 
mouth,  where  they  are  swallowed.  While  the  animal  is  thus  occupied, 
other  Paramecia  in  their  headlong  course  may  strike  against  it.  But 
now  it  does  not  react  to  such  a  shock  at  all ;  it  remains  in  place,  engaged 
with  its  food  taking.  After  the  animal  has  been  in  this  position  for  some 
time,  the  sun  begins  to  shine  strongly  on  this  part  of  the  pool,  heating 
the  water.  All  the  free-swimming  Paramecia  in  this  region  thereupon 
begin  to  swim  rapidly  about,  repeatedly  backing  and  trying  new  direc- 
tions, till  a  direction  is  found  that  leads  to  a  cooler  region.  But  our 
Paramecium,  busy  with  its  food-getting,  does  not  react  to  the  heat  at 
all.  The  water  becomes  hotter  and  hotter,  and  after  a  time  our  infuso- 
rian moves  about  a  little,  turning  over  or  shifting  its  position,  but  still 
remaining  against  the  zooglcea.  All  the  free  swimming  specimens  have 
left  this  region  long  ago.  As  the  water  becomes  still  hotter,  our  Para- 
mecium suddenly  leaves  the  mass  of  zooglcea  and  now  dashes  about 
frantically  under  the  influence  of  the  great  heat.  It  first  swims  back- 
ward, then  forward,  and  tries  one  direction  after  another.  Fortunately 
one  of  these  directions  soon  lead  it  toward  a  cooler  region.  In  this 
direction  it  continues  and  its  behavior  becomes  more  composed.  It 
now  swims  about  quietly,  as  it  did  at  first,  till  it  finds  another  mass  of 
bacteria  and  resumes  the  process  of  obtaining  food. 

In  this  way  the  daily  life  of  the  animal  continues.     It  constantly 
feels  its  way  about,  trying  in  a  systematic  way  all  sorts  of  conditions, 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  107 

and  retiring  from  those  that  are  harmful.  Its  behavior  is  in  principle 
much  like  that  of  a  blind  and  deaf  person,  or  one  that  feels  his  way 
about  in  the  dark.  It  is  a  continual  process  of  proving  all  things  and 
holding  to  that  which  is  good. 

5.     FEATURES   OF    GENERAL    SIGNIFICANCE  IN    THE    BEHAVIOR  OF 

PARAMECIUM 

A.    The  Action  System 

Passing  in  review  the  behavior  of  Paramecium,  we  find  that  the 
animal  has  a  certain  set  of  actions,  by  some  combination  of  which  its 
behavior  under  all  sorts  of  conditions  is  made  up.  The  number  of 
different  factors  in  this  set  of  actions  is  small,  and  they  are  combined 
into  a  coordinated  system,  so  that  we  may  call  the  whole  set  taken 
together  the  action  system.  The  action  system  of  Paramecium  is  based 
chiefly  on  the  spiral  course,  with  its  three  factors  of  forward  movement, 
revolution  on  the  long  axis,  and  swerving  toward  the  aboral  side.  The 
behavior  under  most  conditions  is  determined  by  variations  in  these 
three  factors.  Such  variations,  combined  in  a  typical  manner,  produce 
what  we  have  called  the  avoiding  reaction.  Other  elements  in  the  action 
system  are  the  resumption  of  forward  movement,  in  response  to  stimula- 
tion, and  the  coming  to  rest  against  solid  objects  in  what  we  have  called 
the  positive  contact  reaction.  Subordinate  activities,  playing  little  part 
in  the  behavior,  are  the  contractions  of  the  ectosarc  and  the  discharge 
of  trichocysts. 

The  action  system  thus  includes  only  a  small  number  of  definite 
movements.  By  one  or  another  of  these,  or  by  some  combination  of 
them,  we  may  expect  the  organism  to  respond  to  any  stimulus  which 
acts  upon  it.  We  cannot  expect  each  kind  of  stimulation  to  have  a 
specific  effect,  different  from  that  produced  by  other  stimuli,  for  all 
any  stimulus  can  do  is  to  set  in  operation  certain  features  of  the  action 
system.  Many  different  stimuli  acting  on  this  one  organism  therefore 
necessarily  produce  the  same  effect.  Different  organisms  have  different 
action  systems,  so  that  the  same  agent  acting  on  different  organisms  may 
produce  entirely  different  effects.  The  nature  of  the  behavior  under 
given  conditions  depends  as  much  (or  more)  on  the  action  system  of  the 
animal  as  on  the  nature  of  the  conditions.  In  studying  the  behavior 
of  any  organism  the  most  important  step  is  therefore  to  work  out  its 
action  system,  —  the  characteristic  set  of  movements  by  which  its 
behavior  under  all  sorts  of  conditions  is  brought  about. 

The  most  important  features  of  the  action  system  of  Paramecium 


108  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

are  those  shown  in  what  we  have  called  the  avoiding  reaction.  This, 
as  we  have  seen,  consists  essentially  in  reversing,  stopping,  or  slowing 
up  the  forward  motion,  then  swerving  more  than  usual  toward  the  aboral 
side,  while  at  the  same  time  the  rate  of  revolution  on  the  long  axis  is 
decreased.  By  this  combination  of  movements  Paramecium  responds 
to  most  effective  stimuli  that  act  upon  it.  By  it  are  produced  both 
negative  and  positive  reactions. 

B.    Causes  of  the  Reactions,  and  Effects  produced  by  them 

Examination  has  shown  us  that  the  cause  for  this  reaction  is  some 
change  in  the  conditions;  usually  some  change  in  the  relation  of  the 
animal  to  the  environmental  conditions.  Such  changes  are  brought 
about  chiefly  by  the  movements  of  the  animal.  In  certain  cases 
they  are  due  to  the  direction  of  movement,  carrying  the  animal  into 
environmental  conditions  which  stimulate  it ;  in  other  cases  they  are 
due  to  the  axial  position  taken  by  the  animal,  this  resulting  in  internal 
or  external  disturbances  which  act  as  stimuli. 

These  stimuli  produce,  as  we  have  seen,  not  a  single,  simple,  definitely 
directed  movement,  comparable  to  the  typical  reflex  act.  On  the  con- 
trary, stimulation  is  followed  by  varied  movements,  made  up  of  several 
simultaneous  or  successive  factors,  each  of  which  may  vary,  as  we  have 
seen  in  detail,  more  or  less  independently  of  the  others.  These  move- 
ments produce  varied  effects,  as  follows:  (i)  They  place  the  animal 
successively  and  in  a  systematic  way  in  many  different  axial  positions 
(see  Fig.  38);  (2)  they  cause  it  to  move  successively  and  systemati- 
cally in  many  different  directions;  (3)  they  subject  it  successively 
to  many  different  environmental  conditions,  —  of  temperature,  light, 
chemicals,  mechanical  stimuli,  etc.  Now,  it  is  evident  that  in  this  way 
the  animal  is  practically  certain  to  reach  finally  a  position,  direction  of 
movement,  or  environmental  condition,  that  removes  the  cause  of  stimu- 
lation, since  the  latter  was  due  to  something  wrong  in  one  of  these 
respects.  The  reaction  then  ceases,  since  its  cause  has  ceased;  the 
animal  therefore  retains  the  axial  position,  direction  of  motion,  or  en- 
vironmental condition  thus  reached.  The  method  of  reaction  is  then 
of  such  a  character  as  to  bring  about  whatever  is  required  for  putting 
an  end  to  the  stimulation,  —  whether  this  requirement  is  one  of  orienta- 
tion, of  general  direction  of  locomotion,  or  of  the  retention  of  certain 
environmental  conditions. 

Thus  the  behavior  and  reactions  of  Paramecium  consist  on  the  whole 
in  performing  movements  which  subject  the  organism  to  varied  condi- 
tions (using  this  word  in  the  widest  sense),  with  rejection  of  certain  of  these 


THE  BEHAVIOR   OF  INFUSORIA;  PARAMECIUM  109 

conditions,  and  retention  of  others.  It  may  be  characterized  briefly 
as  a  selection  from  among  the  varied  conditions  brought  about  by  varied 
movements. 

The  fundamental  question  for  this  method  of  behavior  is,  Why  does 
the  organism  reject  certain  conditions  and  retain  others?  We  find 
that  the  animal  rejects,  on  the  whole,  such  things  as  are  injurious  to  it, 
and  accepts  those  that  are  beneficial.  There  are  perhaps  some  excep- 
tions to  this,  but  these  are  rare  and  only  noticeable  because  exceptional ; 
in  a  general  view  the  relation  of  rejection  and  acceptance  to  injury  and 
benefit  is  evident.  It  results  in  keeping  the  animals  from  entering 
temperatures  that  are  above  or  below  those  favorable  for  the  life  pro- 
cesses, in  causing  them  to  avoid  injurious  chemicals  of  all  sorts,  in  saving 
them  from  mechanical  injuries,  and  in  keeping  them  in  regions  con- 
taining food  and  oxygen.  Clearly,  the  animal  rejects  injurious  things, 
and  accepts  those  that  are  beneficial. 

How  does  this  happen?  We  meet  here  the  same  question  that  we 
find  in  higher  organisms  and  man.  How  does  it  happen  that  in  man 
the  response  to  heat  and  cold  beyond  the  optimum  is  by  drawing  back, 
just  as  it  is  in  Paramecium?  How  does  it  happen  that  in  both  cases 
there  is  a  tendency  to  reject  things  injurious  and  retain  things  bene- 
ficial? We  shall  attempt  in  a  later  chapter  to  bring  out  the  relations 
involved  in  this  problem,  in  such  a  way  as  to  make  it  possibly  a  little 
more  intelligible;  here  we  shall  content  ourselves  with  pointing  out 
the  identity  of  the  problem  in  the  infusorian  and  in  man. 

LITERATURE  VI 

A.  Interference  between  contact  and  other  stimuli:  Putter,  1900;  Jennings, 
1897,  1904  h. 

B.  Heat  and  other  stimuli:  Mendelssohn,  1902  a;  Massart.  1901  a. 

C.  Gravity  and  other  stimuli :  Sosnowski,  1899  ;  Moore.  1903. 

D.  Behavior  in  conjugation :  Jennings,  1904/2;  Balbiani,  1861. 


CHAPTER  VII 
THE   BEHAVIOR   OF   OTHER   INFUSORIA 

Action  Systems.    Reactions  to  Contact,  to  Chemicals,  to  Heat 

and  Cold 

The  infusoria  form  a  large  and  varied  group  of  organisms.  In 
the  present  chapter  we  shall  try  to  show  how  far  the  behavior  of  Para- 
mecium is  typical  for  the  group,  and  to  bring  out  important  differences 
found  in  the  behavior  of  other  species.  Certain  features  of  behavior 
are  better  illustrated  in  other  infusoria  than  in  Paramecium ;  these  we 
shall  treat  in  detail.  This  is  notably  true  of  the  reactions  to  light,  and 
to  a  less  degree  of  the  reactions  to  certain  other  stimuli.  Certain 
infusoria  are  much  more  favorable  for  a  study  of  the  modifiability  of 
reactions  than .  Paramecium,  so  that  we  shall  examine  these  relations 
with  care. 

I.    THE   ACTION   SYSTEM 

We  found  that  Paramecium  has  a  certain  set  of  ways  of  acting,  — 
of  "habits,"  one  might  call  them,  — of  which  its  behavior  under  most 
conditions  is  made  up.  These  are  few  in  number  and  combined  into 
a  connected  system,  which  we  have  called  the  "action  system."  The 
action  system  of  Paramecium  is  typical  of  what  we  find  throughout  the 
infusoria,  including  both  the  flagellates  and  the  ciliates.  But  it  becomes 
modified  among  different  species,  in  accordance  with  their  varying 
structure  and  the  conditions  under  which  they  live.  Practically  all  the 
infusoria  agree  with  Paramecium  in  swimming  in  a  spiral  when  passing 
freely  through  the  water,  and  in  the  fact  that  when  stimulated  they 
turn  toward  a  certain  side,  defined  by  the  structure  of  the  organism. 
But  some  species  instead  of  swimming  freely  usually  creep  along  sur- 
faces, while  others  are  attached  by  one  end  to  solid  objects,  remaining 
in  the  same  spot  indefinitely.  These  different  methods  of  life  neces- 
sitate changes  in  the  action  system.  We  shall  take  up  briefly  a  number 
of  species,  bringing  out  the  essential  features  of  the  action  system. 

no 


THE  BEHAVIOR   OF  OTHER   INFUSORIA 


in 


A .    Flagellata 


-nu 


The  free  swimming  flagellates  move  in  a  spiral,  keeping  a  certain 
side  of  the  body  always  toward  the  outside  of  the  spiral,1  just  as  Para- 
mecium does.  By  means  of  the  flagella  they  draw  a  cone  of  water  from 
in  front  to  the  anterior  end  of  the  body,  as  happens  in  Paramecium. 
Among  the  flagellates  the  behavior  has 
been  most  precisely  studied  in  Chilomonas 
and  Euglena  (Jennings,  1900,  1900  a 
and  b). 

Chilomonas.  —  Chilomonas  is  an  un- 
symmetrical  organism,  of  an  irregularly 
oblong  form.  The  body  is  compressed 
sideways  and  bears  an  oblique  notch  at  the 
broader  anterior  end  (Fig.  72).  Of  the  two 
anterior  angles  which  He  on  either  side  of 
the  notch,  one  (x)  is  larger  and  lies  more 
to  the  right  than  the  other  (y).  From  the 
notch  arise  two  long  flagella,  by  the  aid  of 
which  the  animal  swims.  Chilomonas 
often  occurs  in  uncounted  millions  in  water 
containing  decaying  vegetation. 

In  swimming,  Chilomonas  revolves  on 
its  long  axis,  at  the  same  time  swerving 
toward  the  smaller  of  the  two  angles  at 
the  anterior  end  (Fig.  72,  y).  The  path 
followed  thus  becomes  a  spiral  (Fig.  73). 
The  animal  often  comes  to  rest  against  solid  objects;  it  is  then  attached 
by  one  of  the  two  flagella,  while  the  other  is  free. 

To  most  effective  stimuli  Chilomonas  responds  by  an  avoiding  re- 
action similar  to  that  of  Paramecium.  Its  forward  movement  becomes 
slower,  ceases,  or  is  transformed  into  a  movement  backward.  Then 
the  animal  turns  more  strongly  toward  the  side  which  bears  the  smaller 
angle,  and  finally  starts  forward  again.  Thus  the  path  is  altered.  The 
reaction  consists  essentially  in  pointing  the  anterior  end  successively  in 
many  directions,  toward  one  of  which  the  animal  finally  swims.  The 
different  factors  in  the  reaction  vary  with  the  intensity  of  the  stimula- 
tion,  just  as  they  do  in  Paramecium.  The  reaction  may  be  repeated, 
as  in  the  animal  last  named,  until  it  finally  carries  the  organism  away 
from  the  stimulating  region.     Thus  it  is  clear  that  in  Chilomonas,  as  in 

1  This  was  first  observed  by  Naegeli  (i860). 


Fig.  72.  —  Chilomonas,  side  view. 
c.  v.,  contractile  vacuole;  ft,  flagella; 
g,  gullet;  nu,  nucleus;  x,  dorsal  or 
upper  lip;  y,  ventral  or  lower  lip. 


112 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


Paramecium,  the  method  running  through  the  behavior  is  that  of  the 
selection  of  certain  conditions  through  the  production  of  varied  move- 
ments. When  stimulated  the  animal  "tries"  many  different  directions 
till  one  is  found  in  which  stimulation 
ceases.  This  reaction  is  known  to  be  pro- 
duced in  Chilomonas  by  heat,  by  the 
drying  up  of  the  water  containing  the 
animals,  by  mechanical  stimulation,  by 
various  chemicals,  by  passage  from  water 
containing  certain  chemicals  (acid)  to  water 
containing  none,  and  by  the  electric  cur- 
rent. We  shall  take  up  certain  details  of 
the  reactions  of  Chilomonas  in  the  sec- 
tions which  deal  with  the 
different  classes  of  stimuli. 
Euglena.  —  Euglena 
viridis  (Fig.  74),  like 
Chilomonas,  swims  in  a 
spiral.  The  larger  lip 
(Fig.  74,  x)  is  always 
toward  the  outer  side  of 
the  spiral  (Fig.  94). 
When  stimulated  by  com- 
ing in  contact  with  a  weak 
chemical,  by  a  mechanical 
shock,  or  by  a  change  in 
the  intensity  of  light,  Eu- 
glena responds  by  an 
avoiding  reaction  similar 
to  that  of  Paramecium 
and  Chilomonas.  The 
Fig.     74.  —  Eu-  forwar(j  motion  becomes 

glena      viridis,      after 

Kent,    c  v.,  reservoir  slower,   ceases,   or   (more 
of  the  contractile  vacu-  rareiy)      Js     transformed 

ole;    e,    eye    spot;     g,  .  ■" 

gullet;  nu,  nucleus;  x,  mto  a  backward  motion. 

larger  or  upper  lip.  Then  fae  organism 

swerves  more  strongly  than  usual  toward  the  larger  lip.  Thus  the 
spiral  becomes  wider  and  the  organism  becomes  pointed  successively 
in  many  directions  (see  Fig.  91).  In  one  of  these  directions  it  finally 
swims  forward,  repeating  the  reaction  if  again  stimulated.  We  shall 
have  occasion  to  describe  in  detail  the  reactions  of  Euglena  to  light 
(Chapter  VIII). 


Fig.  73.  —  Spiral  path  of 
Chilomonas.  a,  b,  c,  d,  suc- 
cessive positions  occupied. 


THE  BEHAVIOR   OF   OTHER   INFUSORIA 


"3 


To  most  very  intense  stimuli  Euglena  responds  by  contracting  into 
a  sphere  and  beginning  to  encyst. 

The  behavior  of  most  other  flagellates  is  not  known  in  detail,  since 
the  organisms  are  usually  very  minute  and  their  precise  movements  can 
be  followed  only  with  much  difficulty.  Cryptomonas  ovata  is  known  to 
respond  to  stimuli  in  essentially  the  same  way  as  Euglena  (Jennings, 
1904  a),  —  the  swerving  being  toward  the  more  convex  surface.  The 
flagellate  swarm  spores  of  various  algae  react  in  much  the  same  way,  as 
is  shown  by  the  descriptions  of  Naegeli  (i860)  and  Strasburger  (1878), 
though  the  precise  details  have  not  been  worked  out  as  they  have  for 
Chilomonas,  Euglena,  and  Cryptomonas.  Naegeli  (/.  c.,p.  101)  describes 
the  behavior  of  the  flagellate  swarm  spores  on  coming  against  a  mechani- 
cal obstacle,  as  follows:  They  swim  backward,  turn  to  one  side,  then 
swim  forward  in  the  changed  direction.  This  is  exactly  what  Chilo- 
monas does,  as  we  have  seen.  Similar  observations  have  been  made 
on  flagellates  by  various  investigators,  but  only  in  the  species  we  have 
named  has  the  side  toward  which  the  organism  turns  been  determined. 

B.    Ciliata 


In  many  free  swimming  ciliates  the  action  system  is  known  to  be 
essentially  similar  to  that  of  Paramecium.  All  swim  in  spirals,  swerv- 
ing toward  a  certain  side,  and  react  to  stimuli  by  backing  and  swerving 
more  than  usual  toward  a  structurally  defined  side.      Loxodes  rostrum 


Fig.  75.  —  Reaction  of  Loxo- 
phyllum  meleagris.  1-4,  succes- 
sive positions. 


Fig.  76.  —  Methods  of  reaction  to  strong  stimuli 
in  Stentor.  The  individual  at  1  is  stimulated;  it  there- 
upon swims  backward  (2,  3),  turns  toward  the  right 
aboral  side  (3,  4),  and  swims  forward  (5). 


in  reacting  turns  toward  the  aboral  side.  Loxophyllum  meleagris  re- 
acts as  a  rule  by  turning  toward  the  oral  side  (Fig.  75).  Stentor  poly- 
morphic, Stentor  caruleus,  and  Stentor  rceselii  (Fig.  31,  b),  when  free 
swimming,  react  by  turning  toward  the  right  aboral  side  (Fig.  76).  Bnr- 
saria  truncatella  reacts  to  most   stimuli  by  swimming  backward   and 


H4 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


turning  toward  the  right  side  (Fig.  77).  Spirostomum  amhiguum  and 
Spirostomum  tenue  swim  backward  and  turn  toward  the  aboral  side. 
Opalina  ranarum  turns  toward  the  more  convex  (right)  side,  Nycto- 

therus  toward  the  aboral  side 
(Fig.  78).  Many  of  these  or- 
ganisms show  an  additional 
reaction  to  strong  stimuli,  con- 
sisting in  a  marked  contraction 
of  the  body.  This  is  particu- 
larly noticeable  in  Spirostomum 
and  Stentor. 

Many  of  the  Ciliata  do  not 
as  a  rule  swim  freely  through 
the  water,  but  creep  along  sur- 
faces, keeping  one  side  against 

Fig.  77.  — Reaction  of  Bursaria,  ventral  view,  the    Surface.        This    is    true    at 
i-5,  successive  positions  occupied.  tjmes  Qf    mQst  Qf    tJle  organisms 

mentioned  in  the  foregoing  paragraph.  It  is  much  more  usual  in  cer- 
tain other  ciliates,  belonging  to  the  group  of  Hypotricha  (Fig.  31,  /; 
Fig.  81).  In  these  animals  the  cilia  of  one  side  of  the  body  are  spe- 
cially modified  for  creeping,  while  the  opposite  side 
bears  either  few  and  weak  cilia  or  none  at  all.  The 
Hypotricha  are  usually  found  running  about  on  the 
bottom,  or  on  the  surface  of  objects  in  the  water. 
In  addition  to  their  creeping  movements,  they  pro- 
duce by  means  of  strong  peristomal  cilia  a  vortex 
leading  back  to  the  mouth.  These  animals  of  course 
do  not  revolve  on  the  long  axis  as  they  progress,  and 
the  corresponding  feature  is  likewise  lacking  in  the 
reactions  to  stimuli.  On  coming  in  contact  with  an 
obstacle,  or  when  otherwise  stimulated,  they  stop  or   ,    FlG-  j}-~  N-vct°- 

7  1  therus.       1  he  arrow  to 

move  backward  a  distance,  then  turn  toward  a  cer-  the   right  shows    the 
tain  structurally  marked  side,  keeping  in  contact  with  direction  of  turning  in 

J  '  1       °  .       response     to     stimula- 

the  substratum  and  not  revolving  on  the  long  axis,  tion,  while  the   three 
This    renders  it  much  easier  to  observe  the  precise  interjor  arrows  indicate 

1  the  direction  of  beat  of 

method  of  reacting  than  in  Paramecium,  where  the  the  cilia.  After  Dale 
rapid  revolution  on  the  long  axis  is  very  confusing,  to01)- 
As  examples  of  the  creeping  infusoria,  the  following  may  be  mentioned :  — 
Stylonychia  (Fig.  31,  /),  Oxytricha,  and  other  Hypotricha  react  to 
most  stimuli  by  moving  backward  and  turning  to  the  right  (Fig.  79). 
These  organisms  are  particularly  favorable  for  the  study  of  the  reaction 
method.     The  body  is  flat,  and  the  right  and  left  sides  are  very  easily 


THE   BEHAVIOR   OF  OTHER   INFUSORIA 


"5 


Fig. 


view. 


79.  —  Reaction    of    Oxytricha,    ventral 
4,  successive  positions. 


distinguished,  so  that  the  direction  of  turning  after  stimulation  can  be 
determined  with  the  greatest  ease.  In  many  respects  the  Hypotricha 
are  among  the  most  favorable  objects  to  be  found  among  unicellular 
animals  for  studying  behavior. 

Microthorax  sulcatus  usually  creeps  along  the  bottom,  and  reacts  to 
most  stimuli  by  turning  suddenly  toward  the  convex  ("dorsal")  edge. 
The  turning  may  or  may  not  be 
preceded  by  a  start  backward. 

Colpidium  colpoda  (Fig.  31, 
d)  usually  moves  forward  with 
one  side  against  the  substratum, 
following  a  curve  with  its  oral 
edge  on  the  concave  side  of  the 
curve.  When  stimulated  me- 
chanically or  chemically,  it  turns 
toward  the  aboral  side  and  con- 
tinues its  course  (Fig.  80). 

In  some  cases  the  reaction  to  strong  stimulation  takes  on  special 
features.  For  example,  in  Pleuronema  chrysalis,  in  Halteria  grandi- 
nella,  and  in  various  Hypotricha,  there  are  powerful  bristle-like  cirri, 

by  means  of  which  the  animal 

may  leap  suddenly  backward 

or    to    one    side.      These  are 

/  .Arr  "*  u^     <<<<%    >v  probably    to     be     considered 

strongly  marked  avoiding  re- 
actions, not  differing  in  prin- 
ciple from  what  we  find  in 
Paramecium  or  Oxytricha. 

All  the  species  which  usu- 
ally move  along  on  a  surface 
may  at  times  swim  freely 
They  then  as  a  rule  revolve  on  the  long  axis,  both 
when  progressing  and  in  the  avoiding  reaction.  On  the  other  hand, 
almost  all  the  species  which  characteristically  swim  freely  through  the 
water  do  at  times  move  along  surfaces.  They  may  then  react  to 
stimuli  in  the  same  way  as  do  the  Hypotricha.  Such  forms  as  Bursaria 
and  Loxophyllum  are  transitional  between  the  free  swimming  species 
and  those  that  creep  along  surfaces;  they  are  found  about  as  often  in 
one  situation  as  in  the  other. 

In  the  Ciliata  thus  far  considered  the  reaction  method  is  evidently 
that  of  the  selection  of  certain  environmental  conditions  through  the 
productions  of  varied  movements.     When  its  movement  leads  to  stimu- 


Fig.  80.  —  Path  of  Colpidium.  At  2  it  is 
slightly  stimulated;  it  thereupon  turns  toward  the 
aboral  side  (3-4)  and  continues  its  curved  course. 


through  the  water. 


u6  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

lation,  the  animal  responds  by  trying  many  new  directions,  till  one  is 
found  which  does  not  lead  to  stimulation.  The  reaction  is  less  flexible 
in  the  ciliates  which  creep  along  surfaces  than  in  the  free  swimming 
ones.  In  the  former,  owing  to  the  lack  of  revolution  on  the  long  axis, 
all  the  directions  tried  he  in  a  single  plane.  But  under  many  powerful 
stimuli  even  these  species  usually  leave  the  surface  on  which  they  are 
moving;  they  then  react  in  the  freer  way  characteristic  of  unattached 
organisms,  trying  directions  lying  in  many  different  planes. 

There  exists  also  a  large  number  of  ciliates  which  become  more  or 
less  permanently  attached  by  the  part  of  the  body  opposite  the  mouth. 
This  attached  portion  is  usually  drawn  out  to  form  a  slender  stalk  or 
foot.  Examples  of  such  infusoria  are  Stentor  (Fig.  31,  b)  and  Vor- 
ticella  (Fig.  31,  c).  Some  of  these  species  are  found  attached  under 
all  usual  conditions ;  such  are  Vorticella  and  Carchesium.  Others  are 
frequently  found  swimming  freely;  this  is  the  case,  for  example,  with 
Stentor  cceruleus.  Some  infusoria  become  fixed  in  only  a  temporary 
way,  by  a  mucous  secretion.  Such  are  Spirostomum  and  Urocentrum, 
which  are  often  found  suspended  from  solid  objects  by  a  thread  of 
mucus  (Fig.  82).  Even  the  species  which  are  most  firmly  fixed  may 
under  powerful  stimuli  detach  themselves  and  swim  away.  The  heads 
of  Vorticella  and  Carchesium  thus  at  times  detach  themselves  from  their 
stalks  and  swim  about  like  Paramecium.  At  such  times  they  may  also 
creep  over  surfaces,  just  as  do  the  Hypotricha.  The  behavior  when  free 
is  essentially  similar  in  its  main  features  to  that  of  Paramecium  or 
Oxytricha. 

In  the  attached  condition  the  mouth  and  peristome  are  usually 
above,  surrounded  by  a  wreath  of  large  cilia.  These  cilia  are  in  con- 
tinual movement,  in  such  a  way  as  to  bring  a  current  of  water  from  above 
to  the  mouth.  Some  fixed  infusoria  contract  at  intervals  with  marked 
regularity,  even  when  there  is  no  external  stimulation.  Such  is  the  case 
in  Vorticella.  The  reactions  to  stimuli  are  much  modified  as  compared 
with  those  of  the  free  swimming  species.  The  avoiding  reaction  be- 
comes broken  up  into  a  number  of  factors,  any  one  of  which  may  take 
place  more  or  less  independently  of  the  others.  Thus,  Stentor  reeselii 
may  respond  to  stimulation  either  by  a  reversal  of  the  cilia,  driving  away 
the  water  currents,  by  bending  over  toward  the  right  aboral  side,  or  by 
withdrawing  into  its  tube.  Each  of  these  reactions  corresponds  to  a 
certain  definite  feature  in  the  avoiding  reaction  of  free  infusoria.  Owing 
to  the  disintegration  of  the  avoiding  reaction  into  independent  parts,  the 
behavior  of  these  fixed  infusoria  become  more  varied  and  more  highly 
developed  than  that  of  the  unattached  species.  We  shall  have  occasion 
to  treat  of  this  in  detail  later,  in  our  account  of  the  modiliability  of 
reactions  in  Protozoa. 


THE  BEHAVIOR   OF  OTHER   INFUSORIA  117 

2.      REACTION   TO   MECHANICAL   STIMULI 

In  the  responses  of  infusoria  to  contact  with  solid  objects  we  may 
distinguish  the  same  two  reaction  types  that  we  found  in  Paramecium. 
The  animal  may  react  in  what  might  be  called  a  "negative"  way,  avoid- 
ing the  object,  or  it  may  react  "positively,"  placing  itself  against  the 
solid  body. 

The  negative  response  to  contact  with  solid  bodies  is  the  typical 
"avoiding  reaction."  The  animal  moves  backward,  turns  toward  a  cer- 
tain definite  side,  then  swims  forward  again.  In  other  words,  it  tries 
a  new  direction.  If  this  leads  again  against  the  obstacle,  the  animal 
again  reacts  in  the  same  way,  and  this  is  repeated,  till  through  frequent 
trials  the  obstacle  is  avoided. 

There  are  certain  important  points  regarding  the  relation  of  the  direc- 
tion of  movement  in  this  avoiding  reaction  to  the  part  of  the  body  that  is 
stimulated.  Since  the  animal  usually  swims  forward  under  natural  con- 
ditions, it  will  as  a  rule  come  in  contact  with  large  solid  objects  at  its 
anterior  end.  Further,  small  objects  may  be  carried  by  the  ciliary  cur- 
rents to  the  oral  side.  Thus  the  movement  backward  and  the  turning 
toward  the  aboral  side  in  the  avoiding  reaction  remove  the  animal  from 
the  source  of  stimulation.  But  experimentally  other  parts  of  the  body 
can  be  stimulated.  Thus  in  Oxytricha  (Fig.  79),  we  may  with  the  tip 
of  a  fine  glass  rod  stimulate  either  the  left  (oral),  or  the  right  (aboral), 
side.  In  either  case  the  animal  backs  and  turns  to  the  right.  If  the 
right  side  is  repeatedly  stimulated,  the  animal  continually  wheels  toward 
the  stimulated  side;  if  the  left  side  is  touched,  it  wheels  continually 
away  from  the  stimulated  side.  Thus  the  direction  of  movement  in  the 
reaction  is  not  determined  by  the  side  stimulated,  but  by  the  structural 
relations  of  the  organism.  On  the  other  hand,  if  we  stimulate  the 
posterior  end  sharply,  the  animal  does  not  respond  by  the  typical  avoid- 
ing reaction,  but  simply  runs  forward.  The  direction  of  movement  is  in 
this  case  determined  by  the  part  stimulated.  These  results  have  been 
found  to  hold  also  in  many  other  infusoria. 

Experiments  of  the  kind  just  described  have  shown  that  the  anterior 
end  is  as  a  rule  much  more  sensitive  than  the  remainder  of  the  body 
surface.  A  light  touch,  having  no  effect  at  the  posterior  end,  produces 
a  strong  reaction  when  applied  to  the  anterior  end. 

It  is  a  general  rule  that  unlocalized  mechanical  stimuli,  such  as  are 
produced  by  jarring  the  vessel  containing  the  animals,  have  the  same 
effect  as  stimuli  applied  to  the  anterior  end;  they  induce  the  avoiding 
reaction. 

In  the  positive  contact  reaction,  the  animal  places  itself  in  contact 


n8 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


with  the  solid  object  and  remains  against  it.     It  may  now  continue  quiet, 
while  the  oral  cilia  bring  a  current  of  water  containing  food  to  the  mouth. 

But  sometimes  the  animal 
runs  over  the  surface  of  the 
solid,  using  its  cilia  as  if  they 
were  legs.     This,  as  we  have 

Fig.  81.  — Side  view  of  Stylonychia  creeping  along    Seen,  is   the   Common    method 
a  surface.     After  Putter  (i9oo).  of    locomotion    in   the    Hypo- 

tricha.      A  side  view  of  one  of  the  Hypotricha  while  creeping  along  a 

surface  is  shown  in  Fig.  81.     In  other  cases  the  animal  secretes  a  layer 

or  thread  of  mucus  and  thereby  attaches 

itself    to    the  solid.     Attached  in  this  way 

by  a  long  thread  (Fig.  82),  Spirostomum 

and  Urocentrum  often  remain  in  a  certain 

position,  revolving  on  the  long  axis.     The 

thread   is   usually  quite   invisible,  but   by 

passing  a  needle  between  the  solid  object 

and  the  animal,   the  latter  may  often  be 

pulled  backward  by  the  thread  of  mucus. 

In  still  other  cases    the  infusorian   reacts 

to  solid  objects  by  fixing  its  posterior  end 

firmly,  remaining   in    this   place   for    long 

periods,  like  a  plant.     How  this  occurs  in 

Stentor  is  described  in  Chapter  X. 

The  contact  reaction  is  often  directed 
toward  very  minute  objects,  as  we  have 
set  forth  in  detail  in  the  case  of  Parame- 
cium. It  then  serves  the  purpose  of  help- 
ing to  obtain  food.  In  some  of  the  fixed 
infusoria  such  behavior  is  especially  strik- 
ing. Thus,  if  a  small  object  touches  gen- 
tly one  side  of  the  disk  of  Stentor,  the 
animal  may  bend  over  toward  it.  This 
reaction  may  be  seen  when  a  small  or- 
ganism in  swimming  about  comes  against 
the  disk  of  the  animal,  then  attempts  to 
swim  away.     The    Stentor   bends   in    that 

...  .  .  .  Fig.  82.  —  Spirostomum  attached 

direction,  so   as   to  keep   in   contact  with  to  the  bottom  by  a  thread  of  mucus 

the     Organism      as     long     as      possible.        At  and  remaining  stationary  with  anterior 

the  same  time,  of  course,  the  ciliary  vor-  c 

tex  tends  to  draw  the  prey  to    the    Stentor's    mouth.      This    reaction 

may  be  produced  experimentally  by  attaching  a  bit  of  soft,  flocculent 


THE  BEHAVIOR   OF   OTHER   INFUSORIA 


119 


debris  to  the  tip  of  a  fine  glass  rod,  and  allowing  this  to  touch  the  disk 
of  Stentor,  then  drawing  it  gently  to  one  side.  The  Stentor  follows  it, 
often  bending  far  over  (Fig.  83).  The  animal  may  thus  bend  in  any 
direction  —  to  the  right,  to  the  left,  or  toward  oral  or  aboral  side. 

When  infusoria  are  in  contact  with  solids,  their  behavior  always  be- 
comes much  modified.  The  spiral  movement  of  course  ceases,  and  the 
reaction  to  many  stimuli  —  especially  such  reactions  as  depend  largely 
on  the  spiral  movement  —  either  cease  or  become  changed.  Animals 
that  when  free  place  the  axis  of  swimming  in  line  with  gravity,  usually 
take  up,  when  in  contact  with  solids, 
any  position  without  reference  to 
gravity.  To  high  temperatures  at- 
tached specimens  respond  much  less 
readily  than  do  free  swimming  ones. 
Stentor  caruleus  responds  readily  to 
light  when  free  swimming,  directing 
its  anterior  end  away  from  the 
source  of  light;  when  attached,  it 
does  not  react  in  this  way.  Many 
infusoria  show  a  modified  reaction 
to  the  electric  current  when  in  con- 
tact with  solids.  The  flagellates 
Chilomonas,  Trachelomonas,  Poly- 
toma,  and  Peridinium  react  readily  to 

the  electric    Current  when    free    Swim-  which  is  pulled  by  the  experimenter  to  the 

ming;    not   at    all   when   in    contact  nght' 

(Putter,  1900,  p.  246).  Most  ciliates  when  in  contact  with  solids  react 
less  readily  to  the  electric  current,  and  frequently  when  the  reaction 
does  occur,  it  is  of  a  different  character  from  usual.  While  free  speci- 
mens place  themselves  in  fine  with  the  current,  attached  infusoria  often 
take  up  a  transverse  or  oblique  position  with  the  peristome  or  oral 
side  directed  toward  the  cathode,  —  just  as  happens  in  Paramecium. 
This  is  true  in  general  for  the  Hypotricha. 

What  is  the  cause  of  the  interference  of  the  positive  contact  reaction 
with  the  reaction  to  other  stimuli  ?  It  is  necessary,  as  we  have  seen  in 
our  discussion  of  this  reaction  in  Paramecium,  to  distinguish  two  factors 
in  the  contact  reaction ;  one  physical,  the  other  physiological.  The 
physical  factor  is  found  in  the  fact  that  the  organism  actually  adheres 
to  the  surface  of  the  solid,  —  in  many  cases,  at  least,  by  means  of  a 
mucous  secretion.  This  physical  adhesion  would  of  course  tend  to  pre- 
vent that  rapid  movement  under  the  influence  of  a  stimulus  which  is 
shown  by  free  individuals.     Thus,  the  animal  might  attempt  to  react 


Fig.  83.  —  Stentor  rceselii  bending  over  to 
remain    in  contact   with    a    shred   of    debris 


120  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

in  the  usual  way,  —  showing  the  same  ciliary  movements  as  free  indi- 
viduals, —  but  might  find  itself  stuck,  and  unable  to  escape.  Doubtless 
sometimes  this  condition  of  affairs  is  realized ;  it  is  described,  for  ex- 
ample, by  Putter  as  present  in  the  reaction  of  attached  specimens  of 
Colpidium  and  some  other  infusoria.  But  in  many  cases  this  physical 
factor  will  not  account  for  the  observed  behavior.  Infusoria  in  contact 
may  take  different  positions  without  difficulty,  and  could  easily  place 
themselves  in  line  with  gravity,  yet  as  a  rule  they  do  not  do  so.  Attached 
Stentors  could  easily  bend  into  a  position  with  anterior  end  away  from 
the  light,  yet  their  position  shows  no  relation  to  the  direction  of  the  light 
rays.  There  is  nothing  in  the  physical  adherence  to  a  surface  that 
should  compel  the  animal  to  take  a  transverse  position  in  the  electric 
current,  rather  than  a  position  parallel  to  the  current,  yet  this  is  what 
occurs  in  attached  specimens.  It  is  clear  that  there  is  a  physiological 
factor  involved.  Contact  with  solids  tends  to  make  the  animal  act  in 
one  way,  the  other  stimulus  in  another;  hence  the  two  must  interfere. 
If  we  object,  as  some  authors  have  done,  to  the  admission  that  the  contact 
reaction  interferes  with  the  reaction  to  other  stimuli,  we  are  compelled 
to  admit  in  any  case  that  the  reactions  to  other  stimuli  do  interfere  with 
the  contact  reaction,  and  one  admission  has  as  much  theoretical  signifi- 
cance as  the  other.  It  is  evident  that  when  two  agents  influencing 
the  organism  in  opposite  ways  act  simultaneously,  the  effect  of  one  must 
give  way  to  that  of  the  other,  or  the  two  must  combine  to  produce  a 
resultant.  It  is  impossible  that  each  should  produce  its  characteristic 
effect.  The  interference  of  the  contact  reaction  with  the  reactions  to 
other  stimuli  is  one  of  the  most  striking  phenomena  to  be  observed  in 
the  behavior  of  these  lower  organisms.  It  is  always  necessary  to  dis- 
tinguish carefully  the  behavior  of  free  swimming  specimens  from  those 
that  are  in  contact  with  surfaces,  for  the  two  differ  radically. 

3.      REACTION   TO   CHEMICALS 

The  reactions  to  chemical  stimuli  take  place  in  all  accurately  known 
cases  through  the  typical  avoiding  reaction.  As  a  rule  the  motor  organs 
of  the  infusoria,  both  flagellates  and  ciliates,  act  in  such  a  way  that  a 
current  of  water  passes  from  in  front  of  the  animal  to  the  anterior  end 
and  mouth,  as  illustrated  for  Paramecium  in  Fig.  35.  Thus  when  a 
chemical  is  dissolved  in  the  water,  a  "sample"  of  it  is  brought  to  the 
most  sensitive  part  of  the  body.  If  the  chemical  is  of  such  a  nature  as 
to  act  as  a  stimulus,  the  animal  swims  more  slowly,  stops,  or  moves 
backward,  turns  toward  the  customary  side  (usually  the  aboral  side), 
until  it  no  longer  receives  the  chemical,  then  moves  forward  in  the  new 


THE   BEHAVIOR   OF  OTHER   INFUSORIA  121 

direction.  Thus  the  region  containing  the  chemical  is  avoided.  In 
many  cases  this  reaction  takes  place  in  a  very  pronounced  manner; 
the  animal  shoots  far  backward,  whirls  rapidly  toward  the  one  side, 
and  repeats  the  reaction  many  times.  In  other  cases  the  reaction  is 
less  pronounced,  and  motion  merely  becomes  a  little  slower  as  long  as 
the  chemical  is  received  in  the  ciliary  current,  while  at  the  same  time 
the  animal  quietly  swings  its  anterior  end  about  in  a  circle  (as  in  Fig. 
37  or  38).  This  continues  until  it  finds  a  direction  from  which  no  more 
of  the  chemical  is  received ;  in  that  direction  it  swims  forward.  If  the 
movements  of  the  animal  are  not  precisely  observed,  the  method  by 
which  the  reaction  occurs  may  in  such  cases  be  easily  misunderstood. 

There  are  various  chemicals  in  which  certain  infusoria  gather,  pro- 
ducing collections  like  those  formed  by  Paramecium  in  acids  (Fig.  43). 
In  all  cases  in  which  the  facts  are  accurately  known,  these  collections 
are  formed  in  the  same  way  as  are  those  of  Paramecia.  The  animals 
enter  without  reaction  into  the  region  where  the  substance  is  present,  then 
respond  by  the  avoiding  reaction  whenever  they  come  to  the  outer  boun- 
dary of  the  area  containing  the  substance.  Thus  every  individual  that 
enters  the  area  of  the  chemical  remains,  and  in  the  course  of  a  longer 
or  shorter  period  a  collection  is  formed  here.  In  many  cases  this  indirect 
method  of  gathering  together  is  strikingly  evident,  and  the  individuals 
may  be  clearly  seen  to  move  about  within  the  area  containing  the  chemi- 
cal, in  the  manner  represented  in  Fig.  44.  If  the  infusoria  observed 
are  very  minute,  so  that  differentiations  of  the  body  are  to  be  seen  only 
with  great  difficulty,  if  their  movements  are  rapid,  and  if  in  the  avoid- 
ing reaction  they  do  not  swim  backward,  but  merely  stop  and  turn 
toward  one  (structurally  defined)  side,  at  the  same  time  revolving  on 
the  long  axis,  then  the  reaction  method  is  not  so  evident  on  a  cursory 
examination.  In  such  cases,  if  the  relation  of  the  direction  of  turning 
to  the  structural  differentiations  of  the  body  and  to  the  revolution  on  the 
long  axis  are  not  carefully  determined,  the  animal  will  be  supposed  to 
turn  directly,  without  variations  of  any  sort,  into  the  chemical.  This 
was  formerly  supposed  to  be  the  universal  method  of  reaction  to  chemi- 
cals. The  cause  for  the  turning  was  supposed  to  be  found  in  the  dif- 
ference in  the  concentration  of  the  chemical  on  the  two  sides  of  the 
organism.  The  animal  turned  directly  toward  the  side  of  greater  con- 
centration ("positive  chemotaxis")  or  of  less  concentration  ("negative 
chemotaxis").  This  method  of  reacting  to  chemicals  is  no  longer  sup- 
posed to  exist  for  infusoria  by  any  one  familiar  with  the  reaction  method 
described  in  the  foregoing  pages,  so  far  as  I  am  aware,  save  in  the  case 
of  certain  very  minute  organisms,  —  fern  spermatozoids,  Saprolegnia 
swarm   spores,  and   the   flagellate   Trepomonas   agilis   (Rothert,    1901, 


122  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

p.  388).  But  it  is  notable  that  in  none  of  these  cases  has  the  relation 
of  the  direction  of  turning  to  the  differentiations  of  the  body  been  ob- 
served, and  this  is  the  crucial  point  for  determining  the  nature  of  the 
reactions.  The  fact  that  it  is  only  for  these  very  difficult  objects  that 
the  direct  turning  is  maintained  must  make  us  cautious  in  accepting 
this  exceptional  result.1 

Let  us  now  leave  the  method  of  reacting,  and  turn  to  certain  more 
general  phenomena.  In  what  chemicals  do  infusoria  gather?  What 
chemicals  do  they  avoid  ? 

In  no  other  infusoria  is  the  behavior  toward  different  chemicals  so 
well  known  as  in  Paramecium.  Chilomonas  collects  in  acids  in  gen- 
eral, and  especially  in  solutions  of  carbon  dioxide,  just  as  Paramecium 
does.  Spontaneous  gatherings  are  often  formed  by  Chilomonas,  and  it 
seems  probable  that  these  are  due,  as  in  Paramecium,  to  the  carbon 
dioxide  produced  by  the  animals  themselves  (Jennings  and  Moore, 
1902).  Cyclidium  glaucoma  and  Colpidium  colpoda  likewise  collect  in 
carbonic  and  other  acids.  Opalina,  Nyctotherus,  and  Balantidium  cn- 
tozoon,  living  in  an  alkaline  medium,  gather  in  acids,  but  if  transferred 
to  an  acid  medium,  they  gather  in  alkali  (Dale,  1901).  Many  other  in- 
fusoria show  no  tendency  to  gather  in  acids.  Loxocephalus  granulosus 
and  Oxytricha  aeruginosa  form  spontaneous  collections  resembling  pre- 
cisely those  of  Paramecium,  but  they  are  not  due  to  the  same  cause. 
These  species  do  not  collect  in  solutions  of  carbon  dioxide,  nor  in  other 
acids.  When  they  are  mingled  with  Paramecia  in  the  same  prepara- 
tion, they  collect  in  one  region,  while  the  Paramecia  collect  in  another. 
It  is  apparent  that  Loxocephalus  and  Oxytricha  produce  some  substance 
to  which  the  collections  are  due,  and  that  this  substance  is  not  carbon 
dioxide.  A  number  of  other  infusoria  form  spontaneous  collections, 
the  cause  of  which  has  not  been  investigated.  Many  of  the  commonest 
species  do  not  form  such  collections. 

There  are  many  chemicals  in  which  one  or  another  species  of  infusoria 
have  been  found  to  collect.  Most  of  the  details  are  of  comparatively 
little  general  interest  from  the  standpoint  of  animal  behavior,  so  that  we 
shall  not  take  them  up  here.  An  excellent  summary  of  these  results  will 
be  found  in  Davenport's  "Experimental  Morphology"  (Vol.  I,  pp.  32-45). 
Certain  general  features  are  important  for  our  purposes ;  these  we  may 
bring  out  briefly. 

First,  from  the  way  the  collections  are  brought  about,  it  is  evident 
that  whether  given  infusoria  tend  to  collect  in  a  certain  solution  or  not 
depends  on  the  nature  of  the  solution  in  which  they  are  already  found. 
This  has  been  illustrated  in   detail  for  Paramecium.     Paramecia  in 

1  For  a  discussion  of  related  points,  see  Chapter  XIV. 


THE  BEHAVIOR   OF   OTHER   INFUSORIA  12? 

strong  salt  solution  collect  in  weak  salt  solutions  or  in  tap  water; 
Paramecia  in  tap  water  collect  in  distilled  water;  Paramecia  in  dis- 
tilled water  collect  in  weak  acids.  In  the  same  way,  if  two  solu- 
tions are  open  to  any  given  infusorian,  they  tend  to  collect  in  that 
one  by  which  they  are  least  repelled.  Thus  "attraction,"  as  deter- 
mined by  the  formation  of  collections,  is  a  relative  matter ;  the  infusoria, 
like  higher  organisms,  often  have  to  put  up  with  merely  that  by  which 
they  are  least  repelled.  To  say  that  a  certain  infusorian  gathers  in  a 
given  substance  A,  therefore,  signifies  little  more  than  that  it  is  less  re- 
pelled by  this  substance  A,  than  by  the  substance  in  which  it  was  found 
at  the  time  the  experiment  was  tried. 

Most  flagellates  and  ciliates  are  repelled  by  strong  solutions  of  chem- 
icals of  almost  all  sorts.  This  is  true  even  for  strong  solutions  of  the 
same  substances  in  which  they  collect  when  the  solutions  are  weak.  In 
such  substances  we  can  therefore  distinguish  an  optimum  concentration. 
Below  the  optimum  the  organisms  are  indifferent,  while  above  the  opti- 
mum they  are  repelled.  Expressing  the  facts  more  concretely,  at  the 
indifferent  concentration  no  reaction  is  caused  when  the  organism  passes 
into  the  solution  or  out  of  it ;  at  the  optimum  concentration  no  reaction 
is  caused  when  the  organism  passes  into  the  solution,  but  the  avoiding 
reaction  is  induced  on  passing  out,  while  at  concentrations  above  the 
optimum  the  organisms  react  at  passing  inward.  The  result  is  then  in 
every  case  that  they  tend  to  gather  in  the  optimum. 

The  reaction  is  in  each  case  caused  by  a  change  from  one  concentra- 
tion to  another.  The  amount  of  change  necessary  to  cause  the  reaction 
has  been  shown,  in  the  case  of  fern  spermatozoids  (Pfeffer,  1884),  to  bear 
a  definite  relation  to  the  concentration  of  the  solution  in  which  the  organ- 
isms are  immersed.  In  other  words,  the  amount  of  change  necessary 
to  cause  the  reaction  varies  according  to  Weber's  law.  Thus  in  the  fern 
spermatozoids  the  concentration  of  malic  acid  necessary  to  produce  a 
collection  of  the  organisms  must  be  about  thirty  times  that  in  which  the 
organisms  are  already  immersed. 

Massart  (1891)  found  that  specimens  of  Polytoma  nvella  in  his  cultures 
were  not  repelled  by  chemicals  even  in  the  strongest  solutions.  Such 
cases  are  very  exceptional ;  other  investigators  have  found  that  even  this 
same  organism  (from  other  cultures)  is  repelled  by  various  chemicals 
(Pfeffer,  1904,  p.  808,  note). 

The  variability  and  inconstancy  of  the  reactions  of  infusoria  to 
chemicals  deserves  emphasis.  Whether  infusoria  of  a  given  species 
react  to  a  certain  chemical  or  not,  and  how  they  react,  depends  upon 
the  past  and  present  conditions  of  existence  of  the  individuals.  The 
general  outlines  of  the  reactions  can  be  determined  for  any  species,  but 


124  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

the  details,  especially  from  a  quantitative  standpoint,  vary  in  accordance 
with  the  environmental  influences  acting  upon  the  individuals  in  question. 

As  a  rule,  infusoria  collect  in  solutions  of  substances  which  may 
serve  them  as  food.  This  is  almost  invariably  true  for  substances  which 
form  the  usual  food  of  the  organism  under  natural  conditions.  When 
the  amount  of  oxygen  present  in  the  water  is  low,  most  infusoria  collect 
about  bubbles  of  air  or  other  sources  of  oxygen. 

Infusoria  sometimes  gather  in  substances  which  do  not  serve  for 
food  or  respiration,  but  which  serve  other  important  purposes  in  the 
physiology  of  the  species  concerned.  Thus,  the  flagellate  spermato- 
zoids  of  ferns  were  found  by  Pfeffer  to  gather  in  solutions  of  malic  acid. 
This  substance  is  found  in  the  fern  prothalli,  and  probably  occurs  in 
the  mouth  of  the  archegonium,  into  which  the  spermatozoids  must  enter 
in  order  that  fertilization  may  take  place.  The  tendency  to  collect  in 
malic  acid  then  doubtless  plays  a  part  in  bringing  about  fertilization  in 
ferns.  The  collection  of  Paramecia  in  carbon  dioxide  seems  to  be  an- 
other case  of  a  reaction  which  is  useful  to  the  organisms,  though  the 
substance  causing  it  does  not  itself  serve  as  food. 

Many  infusoria  collect,  under  certain  circumstances,  in  substances 
which  do  not  serve  as  food  and  are  not  known  to  play  any  useful  part 
in  the  biology  of  the  animal.  Thus,  Pfeffer  found  that  the  flagellate 
Bodo  saltans  gathers  in  most  of  the  salts  of  potassium,  as  well  as  in  various 
salts  of  lithium,  sodium,  rubidium,  caesium,  ammonium,  calcium,  stron- 
tium, barium,  and  magnesium.  This  signifies  only,  as  we  have  already 
seen,  that  they  are  less  repelled  by  solutions  of  these  substances  than 
by  the  fluid  in  which  they  are  situated.  In  most  cases,  as  soon  as 
a  substance  is  sufficiently  concentrated  to  be  injurious  it  becomes 
repellent. 

Whether  the  repellent  effect  of  chemicals  is  due  to  the  chemical 
properties  of  the  solution,  or  to  its  osmotic  pressure,  has  been  rigidly 
determined  only  for  Paramecium.  In  this  animal,  as  we  have  seen,  the 
osmotic  pressure  is  usually  not  the  cause  of  the  reaction.  There  is  much 
evidence  that  this  is  true  for  most  species,  but  accurate  quantitative 
evidence  is  needed  on  this  point. 

4.     Reaction  to  Heat  and  Cold 

Infusoria  in  general  react  to  heat  and  cold  in  much  the  same  way  as 
does  Paramecium,  —  through  the  avoiding  reaction.  The  way  the  reac- 
tion occurs  is  most  easily  seen  in  the  Hypotricha.  The  phenomena  to 
be  observed  are  of  special  interest,  because  they  show  clearly  how  a 
movement  of  a  large  number  of  individuals  in  a  certain  uniform  direc- 


THE  BEHAVIOR   OF  OTHER   INFUSORIA 


I25 


tion  (•'orientation")  may  be  brought  about  by  the  selection  of  varied 
movements. 

The  common  hypotrichan  Oxytricha  Jallax,  abundant  in  vegetable 
infusions,  is  well  fitted  for  the  study  of  this  reaction.  A  large  number  of 
specimens  are  placed  on  a  slide  or  trough.  When  one  end  of  the  trough 
is  gradually  heated 
by  passing  water  at 
a  temperature  of 
40  degrees  beneath 
it,  the  Oxytrichas 
at  this  end  are 
seen  to  become 
very  active,  dart- 
ing about  in  all  di- 
rections (Fig.  84). 
As  the  temperature 
rises,  they  give  the 
avoiding  reaction, 
—  darting  back- 
ward, and  turning 
to  the  right.  This 
is  alternated  with 
rapid  dashes  for- 
ward. Whenever 
a  specimen  passes 
toward  the  warmer 
end  of  the  trough, 
or  when  it  comes 
in  contact  with  the 
sides  or  end,  it  re- 
sponds with  the 
avoiding  reaction. 
But  a  specimen 
passing  away  from 
the  heated  region, 
in  the  direction  of 
the    arrow   at    14 

(Tig.  84),  does  not  Fig.  84.  —  Reaction  of  Oxytricha  to  heat.  The  slide  is  heated  at 
give  the  reaction  tne  enc^  *•  An  Oxytricha  in  position  i  reacts  as  indicated  by  the  arrows, 
i  ...  repeatedly  moving  backward,  turning  to  the  right,  and  moving  forward, 
Utcause  ll  IS  pass-  thus  occupying  successively  the  positions  1-14.  When  it  finally  be- 
ing from  a  hot  to  comes  directed  away  from  the  heat,  as  at  13-14,  it  ceases  to  change  its 
1  .  rpi  direction  of  movement,  but  continues  to  move  straight  ahead,  thus 
COOl  region.    1  ne  reaching  a  cooler  region. 


126 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


react  in 
cold 


this 


region 


result  is  that  all  the  specimens  which  swim  in  any  direction  but  that 
toward  the  cooler  water  are  quickly  stopped  and  turned,  while  all  that 
pass  toward  the  cooler  water  continue  in  that  direction.  Since  all  the 
specimens  in  the  heated  region  are  moving  very  rapidly  and  turning  at 
very  brief  intervals,  in  a  short  time  all  will  have  become  directed 
toward  the  cool  water.  Hence  soon  after  the  water  has  been  heated  at 
one   end  of   the   trough,  a  stream  of  Oxytrichas  will  be  seen  passing 

toward  the  cool  water.  The 
animals  are  all  "oriented"  in 
a  common  direction,  but  the 
orientation  has  taken  place  by 
exclusion  —  through  the  fact 
that  movement  in  any  other 
direction  is  at  once  stopped. 

If  one  end  is  cooled  to  10 
degrees  C.  or  below,  while 
the  other  is  left  at  the  usual 
temperature,  the  Oxytrichas 
same  way  in  the 
hence  they  leave 
it,  as  they  before  left  the  heated 
region.  The  reaction  in  the 
case  of  cold  is  much  less  strik- 
ing and  less  complete  than  that 
produced  by  heat.  This  is  because  the  cold  has  the  effect  not  only 
of  producing  the  avoiding  reaction,  but  also  that  of  making  the  move- 
ments slower,  and  of  finally  benumbing  the  animals,  so  that  they  cease 
to  move.  Thus  it  takes  much  longer  for  the  animals  to  pass  out  of  a 
cold  region  than  out  of  a  warm  region,  and  many  of  them  do  not  suc- 
ceed in  escaping  before  the  cold  has  stopped  their  movements. 

The  reaction  of  Oxytricha  is  essentially  similar  to  that  of  Parame- 
cium. But  in  Oxytricha  the  method  of  reaction  is  much  more  evident, 
because  the  movements  are  slower,  and  there  is  usually  no  revolution  on 
the  long  axis. 

In  many  other  infusoria  the  reaction  to  heat  and  cold  has  been 
shown  to  take  place  in  the  same  manner  as  in  Oxytricha.  In  some 
species  the  individuals  show  this  type  of  behavior,  yet  with  slight  modifi- 
cations that  are  such  as  to  make  the  reaction  quite  ineffective,  so  that 
the  animals  do  not  escape  from  the  heated  region,  and  are  finally  killed. 
This  may  be  observed  in  Bursaria  truncaiella.  If  one  end  of  a  trough 
containing  specimens  of  Bursaria  is  heated,  the  animals  respond  with 
the  avoiding  reaction,  as  Oxytricha  does.      They  begin  to  swim  back- 


Fig.  85.  —  Bursaria  swimming  backward  in  a 
circle  when  heated.     Ventral  view. 


THE  BEHAVIOR   OF   OTHER   INFUSORIA 


127 


ward,  and  at  the  same  time  to  circle  to  the  right  (Fig.  85).  But  they  do 
not  alternate  this  with  movement  forward,  as  Paramecium  and  Oxytricha 
do,  and  they  do  not  revolve  on  the  long  axis.  Bursaria  simply  continues 
the  reaction  once  begun,  and  this  of  course  has  little  tendency  to  remove 
the  organisms  from  the  heated  region.  They  circle  about  till  they  die. 
Among  different  infusoria  all  gradations  may  be  found,  from  the  inef- 
fective reaction  of  Bursaria  through  the  moderately  rapid  but  effective 
behavior  of  Oxytricha  to  the  quick  movements  of  Paramecium,  which 
can  be  followed  only  with  much  difficulty. 

Mendelssohn  (1902)  has  determined  the  optimum  temperature  for  a 
considerable  number  of  infusoria.  He  finds  the  following  values :  Para- 
mecium aiirelia,  24-28  degrees;  P.  bursaria,  23-25;  Pleuronema,  25-27; 
Col  pod  a,  25-31;  Spirostomum  teres,  24-33;  Coleps,  28-31;  Stentor, 
25-28;  Chlorogonium,  23-30.  As  a  rule  the  organism  is  stimulated  by 
temperatures  both  above  and  below  the  optimum,  so  that  it  seeks  the 
optimum  region.  But  in  rare  cases  a  higher  temperature  acts  as  a 
stimulus,  while  a  lower  temperature  does  not.  This  is  true,  according 
to  Mendelssohn,  in  Pleuronema. 

If  the  entire  vessel  containing  the  infusoria  is  heated,  or  if  the  ani- 
mals are  dropped  into  heated  water,  the  avoiding  reaction  is  produced, 
just  as  when  the  heat  is  applied  from  one  side.  The  animals  swim  back- 
ward and  turn  to  one  side.  It  is  thus  evident  that  there  need  not  be  dif- 
ferences of  temperature  in  different  parts  of  the  body  in  order  to  produce 
the  avoiding  reaction.  In  the  experiment  just  mentioned  the  animal 
"tries"  swimming  in  many  different  directions,  but  of  course  does  not 
find  a  direction  that  takes  it  away  from  the  heated  region. 

LITERATURE   VII 
Behavior  of  Infusoria  in  General 

A.  Action  systems,  methods  of  movement  and  reaction  :  Jennings,  1900,  1899  b, 
1902;  Putter,  1904;  Naegeli,  i860;  Rothert,  1901. 

B.  Reactions  to  contact  with  solids:  Putter,  1900. 

C.  Reactions  to  chemicals:  Pfeffer,  1884,  1888;  Massart,  1889,  1891  ; 
Rothert,  1 90 1,  1903;  Garrey,  1900;  Dale,  1901  ;  Greeley,  1904;  Jennings, 
1900^,  1900 />;  Jennings  and  Moore,  1902. 

D.  Reactions  to  heat  and  cold :  Jennings,  1904;  Mendelssohn,  1902,  1902  a, 
1902  b. 


CHAPTER   VIII 
REACTIONS   OF   INFUSORIA   TO   LIGHT   AND   TO   GRAVITY 

i.   Reactions  to  Light 

Like  Paramecium,  most  colorless  infusoria  do  not  react  at  all  to 
light  of  ordinary  intensity.  But  many  species  of  infusoria  are  colored, 
and  these  commonly  react  in  a  decided  manner  even  to  the  light  supplied 
by  the  natural  conditions  of  existence.  Some  react  positively;  they 
gather  in  lighted  regions  or  swim  toward  the  source  of  light.  Others 
are  negative,  avoiding  light  regions  and  swimming  away  from  the  source 
of  light.  We  shall  take  up  as  examples  the  behavior  of  a  negative  or- 
ganism, Stentor  cceruleus,  and  of  a  positive  organism,  Euglena  viridis. 

A.   Negative  Reaction  to  Light:    Stentor  ccerulens 

The  blue  Stentor  is  a  trumpet-shaped  organism,  with  a  circle  of  large 
adoral  cilia  or  membranelke  surrounding  the  large  end  or  peristome. 
This  circle  leads  to  the  mouth,  lying  at  one  side  of  the  disklike  peristome. 
The  remainder  of  the  body  is  covered  with  finer  cilia.1  The  animal  is 
colored  a  deep  blue.  Stentor  is  often  attached  to  solid  objects  by  its 
pointed  end  or  foot,  but  it  is  likewise  found  at  times  swimming  freely. 

We  shall  have  occasion  to  study  the  general  features  of  the  behavior 
of  Stentor,  particularly  when  attached,  in  a  later  section  (Chapter  X). 
Here  we  need  to  recall  only  the  facts  that  in  response  to  strong  stimula- 
tion it  may  contract,  becoming  shorter  and  thicker,  and  that  when  free 
swimming  it  has  an  avoiding  reaction  similar  to  that  of  Paramecium. 
When  stimulated,  it  stops  or  swims  backward,  turns  toward  the  right 
aboral  side,  and  continues  forward  in  the  new  direction  (Fig.  76).  This 
is  the  reaction  produced  by  mechanical  stimulation,  by  heat,  and  by 
chemical  stimulation  acting  either  on  the  anterior  end  or  on  the  body  as 
a  whole.  The  results  of  localized  stimulation  have  shown  clearly  that 
the  anterior  end  or  peristome  is  more  sensitive  than  the  remainder  of 
the  body  surface. 

1  For  a  figure  of  another  species  of  Stentor,  resembling  in  essentials  the  present  one, 
see  Fig.  31,  b. 

128 


REACTIONS  OF  INFUSORIA   TO  LIGHT  AND  TO  GRAVITY 


129 


The  blue  Stentor  tends  to  gather  in  shaded  regions,  and  when  sub- 
jected to  light  coming  from  one  side  it  moves  away  from  the  source  of 
light.  Thus,  if  a  glass  vessel  containing  Stentors  is  placed  near  a  win- 
dow, the  animals  swim  away  from  the  source  of  light,  and  are  soon  found 
to  be  collected  on  the  side  opposite  the  window. 

How  is  this  result  brought  about?  Just  what  is  the  cause  of  the 
reaction  to  light,  and  what  is  the  behavior  of  the  Stentors  in  reaching 
the  shaded  regions  ? 

In  arranging  experiments  which  shall  answer  these  questions,  let  us 
first  try  the  effects  of  sudden  strong  changes  in  the  intensity  of  the  light 
affecting  the  animals.  This  may  be  done 
by  placing  a  flat-bottomed  glass  vessel  con- 
taining many  Stentors  in  a  shallow  layer  of 
water  on  the  stage  of  the  microscope  in  a 
dark  room.  From  beneath,  strong  light  is 
sent  directly  upward  through  the  opening 
of  the  diaphragm  by  means  of  the  substage 
mirror,  while  all  other  light  is  completely 
excluded.  In  this  way  a  circular  area  in 
the  middle  of  the  field  is  strongly  illumi- 
nated, while  the  remainder  of  the  vessel 
containing  the  Stentors  is  in  darkness.1 
The   Stentors   in   the    darkness 


swim 


Fig.  86.  —  Reaction  of  Stentor 
at  passing  from  a  dark  to  a  light 
region  (1-4). 


about  in  all  directions,  but  as  soon  as  one 
comes  to  the  lighted  area  it  at  once  re- 
sponds by  the  avoiding  reaction  —  it  swims  backward  and  turns  toward 
the  right  aboral  side  (Fig.  86,  1-4).  Thus  its  course  is  changed  and 
it  does  not  enter  the  lighted  area.  Since  every  Stentor  reacts  in  this 
way,  the  lighted  area2  remains  empty.  Usually  the  avoiding  reaction 
occurs  as  soon  as  the  anterior  end  of  the  Stentor  has  reached  the 
lighted  region.  In  other  cases  the  entire  Stentor  passes  completely  into 
the  lighted  area,  then  reacts  in  the  usual  manner,  thus  passing  back 
into  the  dark. 


1  By  using  a  projection  lantern  as  the  source  of  light  the  field  of  the  microscope  is 
projected  on  the  ceiling,  or,  by  the  use  of  a  mirror  to  reflect  the  light  at  right  angles,  on 
the  ordinary  projection  screen.  When  thus  projected,  the  behavior  of  the  Stentors  is 
observable  with  the  greatest  ease. 

2  The  light  is  passed  first  through  a  thick  layer  of  ice  water,  in  order  to  remove  the 
heat  as  far  as  possible.  The  fact  that  the  reactions  are  not  due  to  heat  is  shown  in  the 
following  manner.  Specimens  of  Paramecium,  an  organism  which  is  more  sensitive  to 
heat  than  Stentor,  but  is  not  sensitive  to  light,  are  mingled  with  the  Stentors.  The  Para- 
mecia  pass  into  the  lighted  region  without  hesitation,  showing  that  this  region  is  not 
heated  sufficiently  to  affect  them ;  the  heat  then  cannot  affect  the  Stentors. 

K 


13° 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


Thus  an  area  righted  from  below  acts  in  the  same  manner  as  a  region 
containing  a  strong  chemical.  The  animals  keep  out  of  both  by  the 
avoiding  reaction. 

We  may  now  arrange  the  conditions  so  that  the  light  shall  come  from 
one  side,  while  at  the  same  time  differences  in  illumination  shall  exist  in 

different  regions.  This  may 
be  done  by  placing  the  glass 
vessel  containing  the  Sten- 
tors  near  a  source  of  light 
which  falls  obliquely  from 
one  side,  then  shading  a 
portion  of  the  vessel  with  a 
screen.  We  may  first  so 
place  the  screen  that  the 
vessel  is  divided  into  right 
and  left  halves,  at  equal 
distances  from  the  source  of 
light,  but  one  shaded,  the 
other  illuminated  (Fig.  87). 
The  Stentors  are  at  the  be- 
ginning scattered  through- 
out the  dish  and  are 
moving  in  all  directions. 
Stentors  in  the  illuminated 
half  whose  path  lies  in  the 
proper  direction  pass   into 

Fig.   87.  —  Reaction  to  light   in  Stentor.     The  light  the    shaded    region    without 

comes  from  the  left,  as  indicated  by  the  arrows.     5-5  is  a  reaction        Since    nearlv    all 

screen  shading  one  half  the  vessel,  so  that  the  line  x-y  is  ;                .                       ' 

the   boundary   of   the   shadow.     At  b,  1-4,  is  shown  'the  keep   in    motion    for  a    long 

reaction  of  a  Stentor  on  reaching  this  boundary  line,  tirnp  after  an  interval 
(The  dotted  outline  a,  1-4,  shows  the  reaction  that  would 

occur  if  the  light  caused  increased  activity  in  the  cilia  of  nearly  all  Will   have    passed 

the  side  which  it  strikes.)  Jnto        the        shaded        half. 

Stentors  in  the  shaded  half  respond  by  the  avoiding  reaction  as  soon 
as  they  come  to  the  boundary  of  the  lighted  area.  That  is,  they 
swim  backward  and  turn  toward  the  right  aboral  side  (Fig.  87,  b).  Thus 
they  remain  within  the  shaded  area,  and  after  a  short  time  most  of  the 
Stentors  in  the  vessel  are  to  be  found  in  the  shaded  half. 

It  is  evident  that  the  Stentors  do  not  simply  turn  and  swim  parallel 
with  the  light  rays  from  the  source  of  light.  If  this  were  the  method 
of  reaction,  a  Stentor  coming  to  the  boundary  x-y,  Fig.  87,  would  turn 
and  swim  directly  toward  the  side  y.  This  it  does  not  do.  The  direc- 
tion of  turning  depends  upon  the  position  of  the  right  aboral  side ;   the 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND   TO   GRAVITY    131 

animal  may  even  turn  toward  the  source  of  light.  The  essential  point 
is  the  swimming  back  into  the  shaded  region,  without  reference  to  the 
direction  from  which  the  light  comes. 

Similar  phenomena  are  observed  if  the  side  of  the  vessel  next  to  the 
source  of  light  is  shaded,  the  shadow  of  the  screen  reaching  to  the  middle 


Fig.  88.  —  Reaction  of  Stentor  to  light  when  one  half  the  vessel  next  the  source  of  light  is 
shaded  by  a  screen  S-S  (as  indicated  in  Fig.  89).  On  reaching  the  line  x-y,  where  it  would  pass 
into  the  light,  the  animal  responds  as  shown  at  c,  1-5. 

of  the  vessel,  so  that  the  side  farthest  from  the  source  of  light  is  illumi- 
nated (Figs.  88  and  89).  Under  such  circumstances  the  Stentors  gather 
in  the  shaded  area,  next  to  the  window.  A  specimen  in  the  shaded  area 
which  swims  toward  the  lighted  side  is  of  course  moving  when  it  comes 

to  the  boundary  line  in  the  same  direction 
as  the  rays  of  light.      It   nevertheless  re- 
sponds  by    the  avoiding  reaction,  —  stop- 
turning  toward  the  right  aboral  side, 
and    swimming    back    to    the 
shadow.     This  often  happens 
when    the    animal    has    com- 
pletely   passed    the    boundary 
t,      0        c-j     •       t  tu         r»-       •    tk     and     is    entirely     within     the 

Fig.    8q.  —  Side  view  of    the    conditions    in  the  J 

experiment  shown  in  Fig.  88.     The  arrows  show  the    lighted    area     (Fig.  88,    b).      In 

direction  of  the  rays  of  light.  passing    back   into   the    dark- 

ened area  it  now  swims  of  course  directly  toward  the  source  of  light. 

All  together,  then,  our  experiments  thus  far  have  shown  that  the  cause 
of  the  avoiding  reaction  is  the  change  from  darkness  to  light.  At  every 
such  change,  Stentor  responds  by  the  avoiding  reaction ;  that  is,  it  tries 
swimming  in  other  directions  until  it  is  no  longer  subjected  to  the  light. 

Let  us  now  arrange  the  conditions  in  such  a  way  that  all  parts  of  the 


132  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

vessel  are  equally  illuminated  and  the  light  comes  from  one  side.  This 
may  be  done  by  placing  the  Stentors  in  a  glass  vessel  with  plane  sides,  at 
one  side  of  the  source  of  light,  as  a  window  or  an  electric  lamp.  Move- 
ment from  one  part  of  the  vessel  to  another  cannot  cause  a  change  from 
darkness  to  light,  for  all  parts  are  equally  lighted.1    Yet  the  Stentors 


te 


Fig.  90.  —  Method  of  observing  the  reaction  of  Stentor  to  light.     A  and  B  are  two  electric 
lights,  which  can  be  extinguished  or  illuminated  separately. 

usually,  after  a  short  interval,  turn  and  swim  away  from  the  source  of 
light,  after  a  time  reaching  that  side  of  the  vessel  farthest  from  the  lamp 
or  window.  If  the  animals  are  observed  as  they  turn,  it  is  found  that 
the  turning  is  brought  about  through  the  avoiding  reaction.  A  short 
time  after  the  light  is  directed  upon  them,  they  swim  more  slowly  or 
cease  the  forward  movement,  and  begin  to  swerve  more  strongly  toward 
the  right  aboral  side,  thus  swinging  the  anterior  end  about  in  a  circle. 
The  direction  of  movement  thus  becomes  changed ;  in  the  new  direc- 
tion the  animal  swims  forward.  If  its  anterior  end  is  still  not  directed 
away  from  the  source  of  light,  the  avoiding  reaction  is  repeated;  the 
animal  continues  to  try  new  directions  till  the  anterior  end  is  directed 
away  from  the  lighted  side.  In  that  direction  it  continues  to  move,  so 
that  it  finally  comes  to  the  side  opposite  the  window  or  lamp.2 

1  There  is  of  course  an  infinitesimal  difference  in  the  illumination  of  different  parts 
of  the  vessel,  due  to  the  fact  that  one  part  is  nearer  the  source  of  light  than  another. 
The  experiment  succeeds  equally  well  when  the  sun  is  employed  as  the  source  of  light, 
in  which  case  the  difference  of  illumination  in  different  regions  is  practically  infinitely 
minute.  The  reaction  cannot  be  therefore  conceived  as  due  to  these  differences. 
Experiments  show  that  the  differences  in  illumination  necessary  to  produce  reaction 
are  much  greater  than  those  obtaining  in  different  parts  of  a  vessel  thus  lighted  from 
one  side. 

2  The  reaction  may  be  obtained  by  focussing  the  Braus-Driiner  binocular  micro- 
scope on  a  shallow  vessel  of  Stentors  swimming  about  at  random  in  a  diffuse  light,  then 
allowing  a  strong  light  from  an  electric  lamp  or  a  brightly  lighted  window  to  fall  upon 
them  from  one  side.  In  order  to  have  the  reaction  repeated  many  times,  so  as  to  give 
opportunity  for  careful  study,  the  vessel  containing  the  Stentors  may  be  placed  between 
two  electric  lights,  as  in  Fig.  00.  One  of  these  lights  can  be  extinguished  at  the  same 
instant  that  the  other  is  brought  into  action  ;  by  repeating  this  process  the  direction  of 
the  light  rays  is  repeatedly  reversed.  At  each  reversal  the  Stentors  react  in  the  way 
described  in  the  text. 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND   TO   GRAVITY    133 

Why  does  the  animal  react  in  this  way,  even  when  the  vessel  is  not 
divided  into  regions  of  light  and  darkness,  but  is  lighted  from  one  side  ? 
The  essential  problem  is,  Why  does  a  specimen  swimming  transversely 
or  obliquely  to  the  direction  of  the  light  rays  give  the  avoiding  reaction 
and  continue  this  until  the  anterior  end  is  directed  away  from  the 
source  of  light  ? 

To  understand  this,  certain  facts  need  to  be  recalled.  We  know 
that  the  anterior  end  is  much  more  sensitive  than  the  remainder  of  the 
body.  We  know  that  an  increase  in  illumination  causes  the  avoiding 
reaction.  We  know  that  this  is  true  even  when  the  anterior  end  alone  is 
subjected  to  such  a  change.  Now,  Stentor  swims  in  a  spiral  of  some 
width,  so  that  its  anterior  end  swings  always  in  a  circle,  and  is  pointed 
successively  in  many  different  directions.  If  the  animal  is  swimming 
transversely  or  obliquely  to  the  direction  of  the  light  rays,  the  anterior 
end  in  one  phase  of  the  spiral  path  is  directed  more  nearly  toward  the 
source  of  light,  in  another  phase  more  nearly  away  from  it,  so  as  to  be 
partly  shaded,  —  as  is  illustrated  for  Euglena  in  Fig.  94.  The  result  is, 
of  course,  that  the  sensitive  anterior  end  is  subjected  to  repeated  changes 
in  intensity  of  illumination ;  at  one  instant  it  is  shaded,  at  the  next  the 
light  shines  directly  upon  it.  As  we  know  from  other  experiments,  the 
change  from  light  to  darkness  produces  no  reaction,  while  the  changes 
from  darkness  to  light  produce  the  avoiding  reaction.  Every  time, 
therefore,  that  the  anterior  end  swings  into  the  light,  the  avoiding  reac- 
tion is  caused;  the  animal  therefore  swings  its  anterior  end  in  a  large 
circle,  trying  many  directions.  Every  time  it  swings  its  anterior  end 
away  from  the  source  of  light  into  the  shadow  of  its  body,  on  the  other 
hand,  no  reaction  is  produced;  the  position  thus  reached  is  therefore 
retained.  This  process  continues,  the  animal  trying  new  directions 
every  time  its  anterior  end  swings  toward  the  light,  until  in  a  short  time 
the  anterior  end  must  inevitably  become  directed  away  from  the  light. 
In  this  position  the  anterior  end  is  no  longer  subjected  to  changes  in 
illumination,  for  the  axis  of  the  course  coincides  with  the  axis  of  the  light 
rays,  and  the  body  maintains  a  constant  angle  with  the  axis  of  the  course. 
The  amount  of  light  received  by  the  anterior  end  therefore  remains  con- 
stant. Hence  there  is  no  further  cause  for  reaction,  and  the  organism 
retains  the  position  with  anterior  end  directed  away  from  the  source  of 
Hght. 

Attached  specimens  of  Stentor  do  not  become  oriented  with  refer- 
ence to  the  light.  They  may  occupy  any  position  with  reference  to  the 
direction  from  which  the  light  comes,  even  though  the  light  shines  di- 
rectly on  the  anterior  end.  We  have  seen  previously  that  contact  inter- 
feres with  many  of  the  reactions  of  organisms.     But  if  the  animals  are 


134  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

subjected  to  a  sudden,  powerful  increase  in  the  intensity  of  the  light 
falling  upon  them,  they  often  contract  (Mast,  1906),  and  later  bend  in 
various  directions,  till  they  have  become  accustomed  to  the  light. 

To  sum  up,  the  orientation  of  the  free  Stentor  in  line  with  the  light 
rays,  with  its  anterior  end  directed  away  from  the  source  of  light,  is  due 
to  the  fact  that  an  increase  of  illumination  at  the  sensitive  anterior  end 
induces  the  avoiding  reaction.  As  a  necessary  result  the  oriented 
Stentor  swimming  in  a  spiral  path  tries  new  directions  of  movement  until 
it  finds  one  where  such  changes  of  illumination  no  longer  occur.  Such 
a  direction  is  found  only  in  orientation  with  the  anterior  end  directed 
away  from  the  source  of  light.  From  a  knowledge  of  the  spiral  course 
and  the  fact  that  increase  of  illumination  at  the  anterior  end  causes 
the  avoiding  reaction,  this  result  could  be  predicted.  The  reaction  to 
light,  like  that  to  most  other  stimuli,  is  based  on  the  method  of  trial  of 
differently  directed  movements,  till  one  puts  an  end  to  the  stimulation. 

B.    Positive  Reaction  to  Light:    Euglena  viridis 

Euglena  is  not  closely  related  to  Stentor;  it  is  a  flagellate,  while 
Stentor  is  a  ciliate.  If  we  find  similar  principles  governing  the  reaction 
to  light  in  these  widely  separated  organisms,  it  is  probable  that  these 
principles  are  valid  for  the  infusoria  in  general. 

Euglena  viridis  (Fig.  74)  is  a  fish-shaped  green  organism,  often 
found  abundantly  in  the  water  of  stagnant  roadside  pools,  giving  them 
a  green  color.  At  the  anterior  end  is  a  notch  from  which  there  extends 
a  single  long  flagellum,  by  the  lashing  of  which  Euglena  swims.  Within 
the  body  are  chlorophyll  masses,  giving  the  organism  its  green  color. 
Near  the  anterior  end,  close  to  the  side  bearing  the  larger  lip  of  the 
notch,  —  the  "dorsal"  side,  —  is  a  red  pigment  spot,  usually  known  as 
the  eye  spot.  As  we  have  seen  previously,  the  "action  system"  of 
Euglena  resembles  in  essentials  that  of  Paramecium.  It  swims  in  a 
spiral  (Fig.  94),  and  to  most  stimuli  it  responds  by  an  avoiding  reaction 
which  consists  in  stopping  or  backing,  then  turning  more  strongly  than 
usual  toward  the  "dorsal"  side. 

If  the  light  is  not  too  strong,  Euglenae  gather  in  lighted  areas,  and 
when  the  light  comes  from  one  side,  they  swim  toward  the  source  of 
light.  Thus  in  the  culture  jar  the  organisms  are  usually  found  on  the 
side  next  the  window  or  other  source  of  light.  In  very  powerful  light, 
such  as  the  direct  rays  of  the  sun,  however,  Euglena  swims  away  from 
the  source  of  light.     How  is  this  behavior  brought  about  ? 

Let  us  first  study  the  effect  of  changes  in  the  intensity  of  the  light. 
The  Euglenae  are  placed  on  a  slide  in  a  thin  layer  of  water,  and  are  ex- 


REACTIONS   OF  INFUSORIA    TO   LIGHT   AND   TO  GRAVITY    135 


amined  with  the  microscope  in  the  neighborhood  of  a  window.     Soon 
all  the  Euglenae  are  seen  swimming  toward  the  window.     Now  the 


Fig.  91.  —  Diagram  of  the  reaction  of  Euglena  when  the 
light  is  decreased.  The  organism  is  swimming  forward  at  1 ; 
when  it  reaches  2  it  is  shaded.  It  thereupon  swerves  toward 
the  dorsal  side,  at  the  same  time  continuing  to  revolve  on  the 
long  axis,  so  that  its  anterior  end  describes  a  circle,  the  Eu- 
glena occupying  successively  the  positions  2-6.  From  any  of 
these  it  may  start  forward  in  the  directions  indicated  by  the 
arrows. 

light  is  decreased  by  placing  the  hand  or  a 
screen  between  them  and  the  window.  At  once 
all  give  the  avoiding  reaction;  that  is,  they  stop 
or  swim  backward  an  instant,  then  swerve 
strongly  toward  the  dorsal  side,  so  that  the  ante- 
rior end  swings  about  a  circle  (Fig.  91).  If  the 
light  is  decreased  strongly,  the  anterior  end  de- 
scribes a  wide  circle  or  may  even  turn  through 
an  angle  of  180  degrees,  so  that  the  direction 
of  movement  is  reversed.  If  only  a  little  of  the 
light  is  cut  off,  the  anterior  end  describes  only  a 
narrow  circle.  The  organisms  soon  resume  the 
forward  movement,  but  now  the  axis  of  the 
spiral  path  coincides  with  one  of  the  directions 
indicated  by  the  anterior  end  in  swinging  about 


Fig.  92.  —  Change  of 
direction  in  the  spiral  path 
of  the  Euglena,  as  a  result 
of  a  slightly  marked  reac- 
tion. At  a  the  illumination 
is  decreased,  causing  the 
organism  to  swerve  toward 
the  dorsal  side,  thus  widen- 
ing the  spiral  path.  At  b 
the  ordinary  swimming  in  a 
narrow  spiral  is  resumed; 
since  at  this  point  the  organ- 
ism was  necessarily  more 
inclined  to  the  axis  of  the 
spiral  than  before  the  reac- 
tion, the  new  course  lies  at 
an  angle  to  the  previous  one. 


136  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

a  circle.  In  other  words,  the  direction  of  the  path  has  been  changed 
(Fig.  92).  The  whole  action  may  be  expressed  as  follows:  when  the 
light  is  suddenly  decreased,  the  organism  tries  successively  many 
different  directions,  finally  following  one  of  these. 

The  reaction  is  a  very  sharp  and  striking  one,  and  produces  a  most 
peculiar  impression.  At  first  all  the  Euglenae  are  swimming  in  parallel 
lines  toward  the  window.  As  soon  as  the  shadow  of  the  hand  falls  upon 
the  preparation,  the  regularity  is  destroyed ;  every  Euglena  turns  strongly 
and  may  appear  to  oscillate  from  side  to  side.  This  apparent  oscilla- 
tion is  due  to  the  swerving  toward  the  dorsal  side,  combined  with  the 
revolution  on  the  long  axis.  The  organism  swings  thus  first  to  the 
right,  then  upward,  then  to  the  left,  then  down,  etc.  (see  Fig.  91). 

This  reaction  occurs  whenever  the  light  is  decreased  in  any  way. 
Thus,  in  place  of  cutting  off  the  light  coming  from  the  window,  that 
coming  from  the  mirror  of  the  microscope  may  be  decreased  by  closing 
the  iris  diaphragm.  The  Euglenas  react  in  the  manner  above  de- 
scribed, though  they  soon  resume  their  movements  toward  the  window. 
Again,  if  the  light  from  the  window  is  decreased  only  slightly,  the  Eu- 
glena? react  in  the  manner  described,  thus  changing  their  direction  of 
movement ;  very  soon,  however,  they  swim  again  toward  the  window. 
The  same  reaction  occurs  in  Euglenae  that  are  for  any  reason  not  swim- 
ming toward  the  source  of  light.  Even  if  a  specimen  is  swimming  away 
from  the  window,  it  gives  the  avoiding  reaction  in  the  usual  way  when 
the  light  from  the  window  is  decreased. 

It  is  clear  that  the  reaction  is  due  to  the  decrease  in  the  intensity  of 
light,  not  to  a  change  in  the  direction  of  the  light  rays.  In  the  first  and 
second  experiments  mentioned  in  the  preceding  paragraph,  the  Euglenae 
are,  some  time  after  the  light  is  decreased,  swimming  in  the  same  direc- 
tion as  they  were  before,  though  at  the  moment  of  decrease  there  is  a 
reaction. 

Engelmann  (1882)  tried  shading  parts  of  the  body  of  Euglena.  He 
found  that  a  shadow  which  is  cast  on  the  body  of  the  organism  without 
affecting  the  anterior  one-third  produces  no  effect  whatever.  On  the 
other  hand,  a  shadow  affecting  only  the  anterior  tip  —  if  even  only  the 
part  in  front  of  the  eye  spot  —  causes  the  same  reaction  as  shading  the 
entire  body.  Thus  it  is  clear  that  the  anterior  end  is  more  sensitive  to 
light  than  the  remainder  of  the  body.  These  results  of  Engelmann  are 
of  much  importance  for  understanding  the  remainder  of  the  reaction  to 
light. 

If  Euglenae  are  placed  on  a  slide  and  a  certain  spot  is  lighted  from 
below  by  the  mirror  of  the  microscope,  a  dense  collection  is  in  the  course 
of  time  formed  in  the  lighted  region.     Observations  show  that  the  Eu- 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND   TO  GRAVITY    137 

glense  in  the  darker  portion  swim  about  at  random;  many  of  them  thus 
pass  into  the  lighted  region.  There  is  no  reaction  at  passing  from  the 
dark  to  the  light.  In  the  lighted  region  they  likewise  swim  about  in  all 
directions.     But  as  soon  as  an  individual  reaches  the  outer  boundary  of 


^  e 


~^ 


<0^ 


9\ 


^^ 


)a 


'—4 


Fig.  q3.  —  Illustration  of  the  devious  path  followed  by  Euglena  in  becoming  oriented 
when  the  direction  of  the  light  is  reversed.  From  1  to  2  the  light  comes  from  above;  at  2  it 
is  reversed.      The  amount  of  wandering  (a-h)  varies  in  different  cases. 


the  lighted  area,  it  gives  the  typical  avoiding  reaction;  it  backs,  turns' 
toward  the  dorsal  side,  and  thus  reenters  the  lighted  area.  This  reac- 
tion frequently  occurs  as  soon  as  the  anterior  tip  is  pushed  into  the  shade. 
In  other  cases  the  reaction  does  not  occur  till  the  Euglena  has  passed 


138 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


completely  into  the  dark;  it 


Fig.  94.  —  Spiral  path  of  Eu- 
glena.  a,  b,  c,  d,  successive  positions 
taken.  The  arrows  at  the  right  in- 
dicate the  direction  of  an  incoming 
force,  as  light,  showing  how  the  rela- 
tion of  the  body  axis  and  the  anterior 
end  to  such  a  force  changes  con- 
tinually. At  d  the  body  axis  is 
nearly  parallel  to  the  lines  of  force, 
and  the  anterior  end  is  directly  illu- 
minated. At  b  the  axis  is  nearly 
transverse,  and  the  sensitive  anterior 
end  is  largely  shaded,  so  as  to  re- 
ceive but  little  light. 


then  turns  and  passes  back  into  the  light. 
At  the  boundary  of  the  lighted  area  the 
organism  is,  of  course,  subjected  to  a  sud- 
den decrease  in  illumination,  and  this,  our 
previous  experiments  have  shown  us,  is  the 
cause  of  the  avoiding  reaction.  Whenever 
lighted  or  shaded  areas  are  open  to  Eu- 
glenae,  the  organisms  gather  in  the  lighted 
areas  in  the  way  just  described. 

If  the  entire  area  containing  the  Eu- 
glenae  is  illuminated  from  one  side,  the 
organisms  swim  toward  the  side  from 
which  the  light  comes.  That  is,  they  be- 
come oriented  with  anterior  end  toward 
the  source  of  light.  If  we  watch  them  as 
they  become  oriented,  we  find  that  the 
orientation  takes  place,  as  in  Stentor, 
through  the  avoiding  reaction.  The  course 
of  events  is  about  as  follows  :  The  Eu- 
glenae  are  swimming  about  at  random  in 
a  diffuse  light,  when  a  stronger  light  is 
allowed  to  fall  upon  them  from  one  side. 
Thereupon  the  forward  movement  be- 
comes slower  and  the  Euglenae  begin  to 
swerve  farther  than  usual  toward  the 
dorsal  side.  Thus  the  spiral  path  be- 
comes wider  and  the  anterior  end  swings 
about  in  a  larger  circle  and  is  pointed 
successively  in  many  different  directions. 
In  some  part  of  its  swinging  in  a  circle 
the  anterior  end  of  course  becomes  directed 
more  nearly  toward  the  light;  thereupon 
the  amount  of  swinging  decreases,  so  that 
the  Euglena  tends  to  retain  a  certain  posi- 
tion so  reached.  In  other  parts  of  the 
swinging  in  a  circle  the  anterior  end  be- 
comes less  exposed  to  the  light ;  thereupon 
the  swaying  increases,  so  that  the  organism 
does  not  retain  this  position,  but  swings 
to  another.  The  result  is  that  in  its  spiral 
course  it  successively  swerves  strongly 
toward   the  source  of  light,   then  slightly 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND   TO   GRAVITY 


139 


away  from  it,  until  by  a  continuation  of  this  process  the  anterior  end  is 
directed  toward  the  light.  In  this  position  it  swims  forward.  The 
course  of  Euglena  in  becoming  oriented  is  shown  in  Fig.  93. 

This  behavior  is  intelligible  when  we  recall  the  effect  of  the  spiral 
course  in  causing  changes  in  the  intensity  of  the  light  affecting  the  an- 
terior end.  The  anterior  end  is,  as  we  have  seen,  the  part  most  sensi- 
tive to  light ;  it  may  be  compared  with  the  eye  of  a  higher  animal.     In  a 


Fig.  95.  —  Diagram  of  the  method  by  which  Euglena  becomes  oriented  with  anterior  end 
toward  the  source  of  light.  At  i  the  organism  is  swimming  toward  the  source  of  light.  When 
it  reaches  the  position  2,  the  light  is  changed,  so  as  to  come  from  the  direction  indicated  by 
the  arrows  at  the  right.  As  a  consequence  of  the  decrease  of  illumination  thus  caused,  the 
organism  swerves  strongly  toward  the  dorsal  side,  at  the  same  time  continuing  to  revolve  on  the 
long  axis.  It  thus  occupies  successively  the  positions  2-6.  In  passing  from  3  to  6  the  illumi- 
nation of  the  anterior  end  is  increased,  hence  the  swerving  nearly  ceases.  In  the  next  phase 
of  the  spiral  therefore  the  organism  swerves  but  a  little,  — from  7  to  8.  But  this  movement 
causes  the  anterior  end  to  become  partly  shaded,  and  this  decrease  of  illumination  again  in- 
duces a  strong  swerving  toward  the  dorsal  side.  Hence,  in  the  next  phase  of  the  spiral  the 
organism  swings  far,  through  9  and  10,  to  11.  Thus  it  continually  swerves  much  toward  the 
source  of  light  and  a  little  away  from  it,  till  it  reaches  the  position  16.  Now  it  is  directed 
toward  the  source  of  light,  and  such  swerving  as  occurs  in  the  spiral  course  neither  increases 
nor  decreases  the  illumination  of  the  anterior  end.  Hence  there  is  no  further  cause  for  re- 
action; the  Euglena  continues  its  usual  forward  movement,  which  now  takes  it  toward  the 
source  of  light. 

Euglena  swimming  obliquely  or  transversely  to  the  rays  of  light,  as  in 
Fig.  94,  the  illumination  of  the  anterior  end  changes  greatly  with  each 
turn  in  the  spiral.  At  d  the  light  is  shining  almost  directly  upon  the 
anterior  end,  while  at  b  the  organism  is  nearly  tranverse,  so  that  the 
anterior  end  is  partly  shaded.  The  effect  is  like  that  of  turning  an  eye 
first  toward  the  sun,  then  away  from  it ;  though  the  movement  is  slight, 


140  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

the  change  in  illumination  produced  is  great.  The  variations  in 
illumination  due  to  the  spiral  course  are  doubtless  much  accentuated 
by  the  fact  that  one  side  of  the  anterior  end  bears  a  pigment  spot,  which 
in  certain  positions  of  the  unoriented  Euglena  cuts  off  the  light.  A 
decrease  of  illumination  causes,  as  we  know,  the  avoiding  reaction ; 
the  anterior  end  swings  in  a  wider  circle  (Fig.  91).  This  still  further 
increases  the  variations  in  the  illumination  of  the  anterior  end.  Every 
time  the  illumination  is  decreased,  this  causes  the  animal  to  swerve  still 
more;  so  that  its  anterior  end  becomes  pointed  in  many  different  direc- 
tions, till  it  comes  into  one  where  such  changes  in  illumination  no  longer 
occur.  Such  a  position  is  found  when  the  animal  is  swimming  toward 
the  source  of  light.  Now  the  axis  of  the  body  retains  always  the  same 
relation  to  the  direction  to  the  rays  of  light,  so  that  the  anterior  end  is 
not  subjected  to  variations  in  intensity  of  illumination.  There  is  then 
no  further  cause  for  reaction.  Orientation  is  thus  reached  by  trying 
various  directions.  This  will  be  best  understood  by  an  examination 
of  Fig.  95,  together  with  its  explanation. 

Euglena  responds  most  readily  to  light  of  a  blue  color  (Engelmann, 
1882).  Passage  from  blue  light  to  light  of  other  colors  has  essentially 
the  same  effect  as  passage  from  stronger  to  weaker  light.  If  the  differ- 
ence between  the  two  is  sufficiently  decided,  Euglena  responds  by  the 
avoiding  reaction  in  passing  to  the  other  color;  it  therefore  remains  in 
the  blue.  If  a  small  spectrum  is  thrown  on  a  slide  containing  many 
Euglenae,  they  gather  in  larger  numbers  in  the  blue,  —  especially  in 
the  near  vicinity  of  the  Frauenhofer's  line  F. 

Very  strong  light,  such  as  direct  sunlight,  has  an  effect  on  Euglena 
precisely  the  opposite  of  that  produced  by  weaker  light.  If  the  organ- 
isms are  subjected  suddenly  to  sunlight,  they  give  the  avoiding  reac- 
tion. They  tend  therefore  to  gather  in  less  lighted  regions.  If  the 
sunlight  falls  upon  them  from  one  side,  they  become  oriented  with  an- 
terior ends  away  from  the  source  of  light,  and  swim  in  that  direction. 
The  orientation  takes  place  in  exactly  the  way  described  above,  save 
that  now  it  is  the  increase  of  light  at  the  anterior  end  that  causes  the 
avoiding  reaction.  If  a  vessel  is  placed  in  such  a  position  that  the  sun 
shines  on  it  from  one  side,  while  the  half  of  the  vessel  away  from  the  sun 
is  shaded  with  a  board,  the  following  result  is  produced :  The  Euglenae 
gather  in  a  band  at  the  edge  of  the  shadow  (Fig.  96).  They  do  not 
pass  into  the  dark  area  beneath  the  shadow,  nor  do  they  remain  in 
the  region  affected  by  direct  sunlight,  but  in  an  area  of  intermediate 
illumination.1 

'This  experiment  is  due  to  Famintzin  (1867,  p.  21). 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND    TO   GRAVITY     141 

We  can  thus  distinguish  an  optimum  intensity  of  light,  in  which 
Euglena  tends  to  remain.  Movement  toward  either  a  greater  or  a  less 
intensity  of  light  causes  the  avoiding  reaction,  with  its  trial  of  different 
positions  and  directions  of  movements, 
till  a  position  or  direction  is  found 
which  leads  toward  the  optimum,  or 
retains  the  optimum  intensity  undi- 
minished. Or,  in  other  words,  after 
Euglena  receives  an  amount  of  light 
which  we  might  call  "enough,"  it 
avoids  more  light,  and  also  less  light. 


That  degree  of  light  in  which  it  tends 


Fig.  96.  —  Diagram  to  illustrate  the 
results  of  Famintzin's  experiment.  The 
light  comes  from  the  direction  indicated 
by  the  arrows,  while  the  opposite  side  of 
the  vessel  is  shaded,  as  indicated  by  the 
dots.  The  Euglenae  gather  in  the  inter- 
mediate region,  across  the  middle. 


to  remain  seems  to  be  about  the 
amount  which  is  most  favorable  to  its 
life  activities.  Euglena  requires  light 
for  assimilating  carbon  dioxide  by  the 
aid  of  its  chlorophyll,  just  as  do  higher  plants.  If  confined  to  dark- 
ness, it  soon  ceases  activity,  contracts  into  a  sphere,  and  becomes  en- 
cysted. On  the  other  hand,  direct  sunlight  is  very  injurious  to  it ;  if 
long  continued  it  causes  the  organism  to  fall  to  the  bottom  and  die. 
Euglena  avoids  both  the  higher  and  the  lower  intensities  that  are 
injurious  to  it. 

C.    Negative  and  Positive  Reactions  compared 

Thus  in  both  negative  organisms  (Stentor)  and  positive  organ- 
isms (Euglena),  the  determining  cause  of  the  reaction  is  a  change  in 
the  intensity  of  light,  and  the  reaction  takes  place  by  the  usual  method  of 
the  performance  of  varied  movements,  subjecting  the  animal  succes- 
sively to  different  conditions.  When  the  sensitive  anterior  end  is  sub- 
jected alternately  to  light  and  shade,  the  organism  "tries"  other  direc- 
tions of  movement  till  it  finds  one  where  such  changes  are  not  pro- 
duced. In  Stentor  it  is  an  increase  in  light  that  causes  this  reaction ; 
in  Euglena  is  it  usually  a  decrease  that  causes  the  reaction,  though 
when  the  light  is  very  strong  an  increase  may  have  the  same  effect. 


D.    Reactions  to  Light  in  Other  Lnjusoria 

The  reactions  of  other  infusoria  to  light  are  similar  in  character, 
so  far  as  known,  to  those  of  Stentor  and  Euglena.  In  only  a  few  other 
cases  have  details  of  the  avoiding  reaction  been  worked  out  as  thoroughly 
as  for  the  two  species  mentioned.  But  all  that  we  know  of  the  reac- 
tions of  infusoria  to  light  is  consistent  with  the  method  of  reaction  known 


142  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

to  exist  in  Stentor  and  Euglena ;  indeed,  the  evidence  seems  clear  that 
these  reactions  take  place  in  essentially  the  same  way  throughout  the 
group.  In  Cryptomonas  ovata,  and  less  completely  in  the  swarm 
spores  of  Chlamydomonas  and  Cutleria,  the  present  writer  has  observed 
that  the  reaction  to  light  is  of  the  same  character  as  in  Euglena.  We 
shall  pass  in  review  certain  general  features  of  the  reaction  in  other 
infusoria,  as  described  by  various  authors. 

As  we  have  before  noted,  most  colorless  infusoria  give  no  indication 
of  sensitiveness  to  light.  But  color  is  not  absolutely  necessary  in  order 
that  reaction  to  light  may  occur,  as  is  shown  by  the  fact  that  Amoeba 
reacts  to  light.  Even  in  the  infusoria,  colorless  species  may  react  to 
light  when  such  behavior  is  distinctly  beneficial  to  the  organism.  A 
species  of  Chytridium,  a  colorless  flagellate  that  is  parasitic  on  the 
green  organism  Haematococcus,  reacts  to  light  in  the  same  manner  as 
Haematococcus,  collecting  as  a  rule  in  lighted  regions,  or  at  the  side  of 
the  vessel  next  the  source  of  light  (Strasburger,  1878).  This,  of  course, 
aids  it  in  finding  its  prey,  which  collects  in  the  same  regions.  Several 
other  colorless  infusoria  that  are  parasitic  on  green  flagellates  have 
been  found  to  react  to  light  in  the  same  manner  as  their  prey.  Ver- 
worn  (1889,  Nachschrift)  found  that  the  colorless  ciliate  Pleuronema 
chrysalis  reacts  to  a  sudden  increase  in  the  intensity  of  light  by  a  rapid 
leaping  movement,  —  evidently  a  strongly  marked  avoiding  reaction. 
Certain  colorless  infusoria  react,  as  we  shall  see  later,  to  ultra-violet 
light. 

In  the  green  ciliate  Paramecium  bursaria  the  reaction  to  light  de- 
pends, according  to  Engelmann  (1882),  on  the  amount  of  oxygen  in 
the  water.  This  animal  contains  chlorophyll,  which  produces  oxygen 
in  the  light.  When  there  is  little  oxygen  in  the  water,  the  organism 
gathers  in  lighted  regions,  thus  of  course  increasing  its  store  of  oxygen. 
When  the  individuals  in  the  light  come  to  the  boundary  of  a  dark  region, 
"they  turn  around  at  once  into  the  light,  as  if  the  darkness  was  unpleas- 
ant to  them"  {I.e.,  p.  393).  The  response  is  thus  clearly  an  avoiding 
reaction,  like  that  of  Stentor.  When  the  water  contains  much  oxygen, 
on  the  other  hand,  Paramecium  bursaria  avoids  the  light.  On  reach- 
ing a  lighted  area  the  animals  react  in  the  way  above  characterized, 
and  return  into  the  darkness.  When  they  gather  in  light,  it  is  especially 
in  the  red  rays  of  the  spectrum  that  they  collect;  these  are  the  rays  in 
which  the  chlorophyll  is  most  active.  When  they  avoid  light,  it  is 
again  the  red  rays  that  are  most  effective  in  producing  the  avoiding 
reaction. 

Hertel  (1904)  found  that  Paramecium  bursaria,  Epistylis  plicatilis, 
Stentor   polymorphous,  and    Carchesium  react    to    ultra-violet  light,  of 


REACTIONS  OF  INFUSORIA    TO   LIGHT   AND    TO   GRAVITY      143 

280  fxfx  wave  length.  In  the  two  species  last  named  the  chief  reaction 
observed  was  a  sudden  contraction.  Epistylis  bends  to  one  side  under 
the  action  of  the  light,  while  Paramecium  bursaria  reacts  in  essentially 
the  same  manner  as  to  ordinary  light,  as  described  above.  All  died 
quickly  under  the  action  of  powerful  ultra-violet  light. 

The  flagellate  swarm  spores  of  many  algas  react  to  light.  Their 
behavior  in  this  reaction  has  been  studied  especially  by  Strasburger 
(1878).  These  swarm  spores  (Fig.  97)  usually  resemble  Euglena  in 
essential  features,  though  they  may  differ  in  form,  in  the  number  of 
flagella,  and  in  other  details.  They  contain  chlorophyll  or  other  color- 
ing matter,  and  usually  a  red  eye 
spot.  The  action  system  of  the 
spores  is  similar  to  that  of  Euglena. 
They  swim  in  a  spiral  path,  keeping 
a  certain  side  always  toward  the  axis 
of  the  spiral  (Naegeli,  i860,  p.  96). 

On   Coming  to  an  obstacle,  they  react  Fig.  97.  —  Examples  of  swarm   spores, 

1       ,  •         ,  •  1      /tvj  v     7      \     after  Schenck.      a,  Hpematococcus  pluvialis; 

by  turning  tO  One  Side  (Naegeli,  U.),  b<  uiothrixzonata;  c,  Botrydium  granulatum, 
with     or     without     a     previous     Start   gamete;   d,  Cladophora  giomerata;   e,  CEdo- 

backward.      It  is  probable  that  the  gomum- 

turning  in  response  to  a  stimulus  is  always  toward  the  side  directed 
outward  in  the  spiral  path,  as  it  is  in  Euglena,  Chilomonas,  and  Cryp- 
tomonas.  The  movements  of  the  swarm  spores,  so  far  as  known,  exactly 
resemble  those  of  the  organisms  just  named.  It  is  further  without 
doubt  true  that  the  anterior  end  is  in  the  swarm  spores,  as  in  other 
infusoria,  the  most  sensitive  part  of  the  body.  The  swarm  spores  are 
much  smaller  than  Euglena,  so  that  the  details  of  the  behavior  are  less 
easy  to  determine. 

Strasburger  found  that  when  the  light  is  weak,  all  the  colored  swarm 
spores  *  swim  toward  the  lighted  side  of  a  drop  (positive  reaction). 
When  the  light  is  strong,  some  swim  away  from  the  lighted  side  (nega- 
tive reaction).  If  different  parts  of  a  drop  or  a  vessel  are  unequally 
illuminated,  the  swarm  spores  gather  in  the  lighted  region.  The  phe- 
nomena are  thus  in  general  similar  to  those  found  in  Euglena.  There 
are  certain  variations  among  the  different  swarm  spores.  Thus,  Stras- 
burger found  that  Botrydium  and  Cryptomonas  are  positive  even  in  the 
strongest  light,  while  in  a  weak  light  Cryptomonas  is  indifferent.  But 
in  most  species  there  is,  as  in  Euglena,  an  optimum.      In  light  below 

1  Strasburger  studied  the  swarm  spores  of  Hsematococcus  lacustris,  Ulothrix,  Chaeto- 
morpha,  Ulva,  Botrydium,  Bryopsis,  (Edogonium,  Vaucheria,  and  Scytosiphon,  as  well 
as  the  flagellate  Cryptomonas  (called  Chilomonas  by  Strasburger),  and  the  colorless 
swarm  spores  of  Chytridium  and  Saprolegnia. 


144  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

the  optimum  they  are  positive ;   in  light  above  the  optimum  they  are 
negative. 

Strasburger  did  not  determine  the  precise  movements  of  the  organ- 
isms in  the  reaction  to  light.  That  is,  he  did  not  determine  toward 
which  side  they  turn  in  becoming  oriented.  But  in  other  respects  his 
account  is  so  excellent  that,  with  the  fuller  results  on  Euglena  as  a  key, 
it  is  not  difficult  to  analyze  out  the  precise  factors  in  the  behavior. 

If  the  light  affecting  the  organisms  is  suddenly  decreased  in  intensity, 
Strasburger  found  that  the  swarm  spores  (Botrydium  and  Ulva)  sud- 
denly turn  toward  one  side  (I.e.,  p.  25).  In  Bryopsis  this  reaction  was 
produced  also  when  the  light  was  suddenly  increased.  In  all  the  swarm 
spores  it  was  evident  that  as  soon  as  the  light  was  decreased  by  the  in- 
terposition of  a  screen  the  path  became  more  crooked  (I.e.,  p.  27). 
In  other  words,  the  spiral  became  wider,  owing  to  the  increased  swerv- 
ing toward  a  certain  side.  In  these  respects  the  swarm  spores  precisely 
resemble  Euglena.  It  is  clear  that  they  react  to  a  sudden  decrease  in 
illumination  by  an  avoiding  reaction,  which  consists  in  turning  more 
or  less  strongly  toward  a  certain  side,  with  or  without  a  cessation  of  the 
revolution  on  the  long  axis;  in  this  way  the  direction  of  progress  is 
changed. 

As  would  be  expected  from  this  method  of  response,  the  organisms 
react  at  passing  from  a  light  to  a  dark  region.  If  a  ring  is  placed  over 
the  drop  containing  the  organisms,  so  that  only  a  central  circle  is  illu- 
minated, the  positive  organisms  gather  in  the  illuminated  circle  (Fig. 
98,  A).  Here  they  swim  toward  the  window  from  which  the  light 
comes,  but  on  reaching  the  edge  of  the  shadow,  they  turn  back  into  the 
lighted  region  (I.e.,  p.  28).  Often  the  organism  passes  completely 
into  the  shadow  before  reacting,  then  it  turns  and  swims  back  into  the 
light.  Thus  it  does  not  react  till  a  short  time  after  the  moment  of  change. 
If  a  narrow  band  of  shadow  passes  across  the  middle  of  the  drop,  trans- 
versely to  the  direction  from  which  the  light  is  coming,  this  usually  does 
not  stop  the  organisms,  because  of  this  interval  of  time  which  elapses 
before  their  reaction ;  before  they  begin  to  react  they  have  passed  com- 
pletely across  the  band  into  the  lighted  region  beyond.  But  if  a  larger 
vessel  is  used  and  a  broader  transverse  band  of  shadow  passes  across 
it  (Fig.  98,  B),  this  does  stop  the  organisms.  They  gather  on  the  edge  of 
the  shadow  without  passing  across  it.  In  many  other  ways  Strasburger 
shows  that  when  the  area  containing  the  swarm  spores  is  unequally 
illuminated,  the  positive  organisms  collect  in  the  more  illumined  region. 
In  this  they  precisely  resemble  Euglena,  as  Strasburger  himself  noted. 
The  behavior  is  of  course  a  direct  result  of  the  production  of  the  avoid- 
ing reaction  by  a  decrease  in  light. 


REACTIONS  OF  INFUSORIA  TO  LIGHT  AND  TO  GRAVITY    145 

If  the  experiments  were  made  with  swarm  spores  that  were  nega- 
tive to  the  intensity  of  light  used,  they  gathered  of  course  in  the  shadow 
instead  of  in  the  light.  If  a  board  was  placed  across  the  middle  of  the 
vessel  from  right  to  left,  such  swarm  spores  formed  a  collection  in  the 
partly  shaded  region  at  the  edge  of  the  board  (as  in  Fig.  96),  where  they 
found  the  optimum  degree  of  illumination.  They  were  repelled  both 
by  the  strong  light  and  by  the  deep  shadow. 

Thus  it  is  clear  that  in  the  swarm  spores,  as  in  Euglena  and  Stentor, 
a  change  in  the  intensity  of  illumination  produces  reaction.  But  a 
certain  amount  of  change  is  required  before  any  effect  is  produced. 
If  the  intensity  of  illumination  changes  only  very  gradually  from  one 


Fig.  98.  —  Diagrams  to  illustrate  the  results  of  some  of  Strasburger's  experiments  with 
positive  swarm  spores  (original).  A,  the  margins  of  the  drop  are  shaded  (as  indicated  by  the 
dots);  the  organisms  gather  in  the  lighted  centre.  B,  a  broad  band  of  shadow  lies  trans- 
versely across  the  drop;  the  organisms  swim  toward  the  light,  but  are  stopped  by  the  shadow. 
Thus  two  groups  are  formed,  one  at  the  side  of  the  drop  next  the  light,  the  other  in  a  corre- 
sponding position  at  the  edge  of  the  shadow. 


region  to  another,  the  difference  in  intensity  between  succeeding  points 
is  insufficient  to  cause  reaction.  Hence  under  these  circumstances  the 
organisms  remain  scattered  and  move  about  without  reaction.  Stras- 
burger  showed  this  in  the  following  way.  He  used  a  hollow  wedge- 
shaped  prism,  20  cm.  long,  tilled  with  a  partly  opaque  solution  of  humic 
acid  in  ammonia.  Through  this  the  light  was  passed.  At  the  thin 
end  of  the  wedge  nearly  all  the  light  was  transmitted ;  at  the  thick  end 
little  or  none,  and  there  was  a  gradual  transition  from  light  to  dark 
between  the  two  ends.  This  prism  was  placed  over  the  drop  contain- 
ing the  swarm  spores,  and  the  light  was  allowed  to  fall  directly  from 
above  (Fig.  99,  X).  The  drop  being  very  small  in  comparison  to  the 
length  of  the  wedge-shaped  prism,  there  was  of  course  but  little  differ- 
ence in  the  illumination  of  its  two  sides,  and  the  transition  from  one 
to  the  other  was  very  gradual.  Under  these  conditions  the  swarm 
spores  remained  scattered  throughout  the  drop.     The  change  in  pass- 


146 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


ing  from  one  region  to  another  was  not  sufficiently  marked  to  cause 
reaction.1 

When  the  entire  area  is  equally  lighted  and  the  light  comes  from 
one  side,  the  positive  swarm  spores  swim  toward  the  source  of  light. 
If  the  light  is  made  strong,  most  species  swim  away  from  its  source. 
In  this  behavior  the  agreement  with  Euglena  is  complete.     The  orien- 


-a 


FlG.  99.  —  Diagram  of  the  conditions  in  Strasburger's  experiments  with  a  wedge-shaped 
prism,  constructed  from  the  data  furnished  by  Strasburger.  a,  prism  20  cm.  in  length,  filled 
with  a  translucent  fluid,  b,  hanging  drop  containing  the  swarm  spores.  X,  rays  of  light 
coming  from  above,  as  in  the  first  experiments.  F,  rays  coming  obliquely  from  the  thicker 
end  of  the  wedge,  as  in  the  second  set  of  experiments.      The  figure  is  one  half  natural  size. 

tation  takes  place  gradually,  by  a  series  of  trials,  as  in  Euglena.  Stras- 
burger paid  no  special  attention  to  this  point,  but  the  present  writer 
has  observed  that  this  is  true  in  Cryptomonas,  Chlamydomonas,  and 
the  swarm  spores  of  the  marine  alga  Cutleria,  as  well  as  in  Euglena, 
and  Strasburger  (1878,  p.  24)  notes  incidentally  that  it  is  true  in  Haema- 
tococcus.2 

It  seems  clear,  then,  that  the  reaction  takes  place  in  the  same  manner 

1  It  is  curious  that  Strasburger  drew  from  this  experiment  the  erroneous  conclusion 
that  variations  in  the  intensity  to  light  play  no  part  in  the  reaction.  The  only  essential 
difference  between  this  experiment  and  the  previous  ones  (Fig.  98)  is  that  in  the  pre- 
vious experiments  the  change  of  illumination  in  passing  from  one  region  to  another 
is  sudden  and  pronounced,  while  in  the  present  experiments  it  is  slow  and  gradual. 
The  logical  conclusion  is  that  the  lack  of  reaction  in  the  present  experiment  is  due  to 
the  slightness  of  the  change  in  passing  from  one  part  of  the  preparation  to  another. 
When  we  consider  that  the  prism  was  20  cm.  in  length,  and  was  placed  over  a  mere 
drop,  it  is  evident  that  the  difference  in  illumination  in  different  parts  of  the  drop 
was  excessively  small.  We  know  that  for  the  effective  action  of  all  stimuli  a  certain 
threshold  amount  of  change  is  necessary,  so  that  the  results  are  exactly  what  might 
be  anticipated.  Our  account  of  Euglena  shows  beyond  doubt  that  a  change  in  intensity 
of  illumination  does  cause  reaction.  Strasburger  himself  (I.e.,  p.  25)  observed  the  same 
fact  in  swarm  spores,  though  he  paid  little  heed  to  this  observation  in  the  remainder  of 
the  work. 

2  He  says  that  when  the  direction  of  the  light  is  changed,  the  swarm  spores  become 
oriented  "  Nach  verschiedenen  Schwankungen." 


REACTIONS   OF  INFUSORIA    TO   LIGHT  AND   TO   GRAVITY    147 

in  the  swarm  spores  as  in  Euglena.  As  set  forth  on  page  139,  the  move- 
ment toward  or  from  the  source  of  light,  in  a  field  of  which  all  parts 
are  equally  lighted,  is  due  to  the  fact  that  in  the  unoriented  individuals 
the  sensitive  anterior  end  is  subjected  to  frequent  changes  in  the  inten- 
sity of  illumination.  It  is  first  directly  lighted,  then  shaded.  These 
changes  induce  reaction.  By  the  method  of  trial  the  organism  then 
comes  into  a  position  such  that  these  changes  cease.  Such  a  position 
is  found  only  in  orientation.  All  these  relations  evidently  hold  equally 
well  for  the  swarm  spores;  for  details  the  reader  may  refer  to  the  ac- 
count of  the  behavior  of  Euglena. 

What  happens  if  the  field  containing  the  organism  is  righted  from 
one  side,  and  there  are  at  the  same  time  variations  in  the  intensity  of 
light  in  different  parts  of  the  field?  Strasburger  devised  certain  ex- 
periments to  answer  this  question.  These  experiments  have  become 
celebrated,  and  an  immense  amount  of  ingenuity  has  been  expended 
in  endeavoring  to  interpret  them  in  one  way  or  another.  Strasburger's 
experiments  involved  the  use  of  the  wedge-shaped  prism  shown  in 
Fig.  99.  This  prism  was  placed  over  the  drop  containing  the  swarm 
spores,  in  such  a  way  that  the  light  came  obliquely  from  the  direction 
of  the  thick  end  of  the  wedge,  as  in  Fig.  99,  Y.  Now  the  intensity  of 
illumination  is  greater  on  the  side  farthest  away  from  the  source  of 
light,  and  decreases  as  we  pass  toward  the  source  of  light.  Will  the 
positive  swarm  spores  move  toward  the  source  of  light,  and  thus  into  a 
region  of  less  illumination,  or  will  they  rather  move  into  the  region  of 
greater  illumination,  and  thus  away  from  the  source  of  light? 

Strasburger  found  that  the  positive  swarm  spores  move  toward  the 
source  of  light,  and  hence  into  the  region  of  less  illumination.  It  is 
extraordinary  that  this  result  should  have  occasioned  the  surprise  and 
comment  which  have  been  bestowed  upon  it.  Strasburger's  previous 
experiment  with  perpendicular  light  (Fig.  99,  X)  had  shown  that  the 
variations  in  intensity  of  illumination  in  different  parts  of  a  drop  under 
this  prism  were  too  slight  to  cause  reaction,  the  organisms  remaining 
scattered  throughout  the  drop.  Evidently  so  far  as  the  organisms  were 
concerned  these  slight  variations  did  not  exist ;  they  were  not  perceived. 
Therefore,  when  the  light  comes  from  one  side,  the  organisms  react 
exactly  as  they  do  when  such  variations  do  not  exist.  They  swim 
toward  the  source  of  light  for  the  same  reason  that  they  do  when  the  prism 
is  not  present.  The  experiment  consists  essentially  in  making  the  differ- 
ences in  the  intensity  in  neighboring  regions  so  slight  that  they  are  un- 
perceived.  We  need  not,  therefore,  be  surprised  that  the  organisms  fail 
to  react  to  them. 

The  experiments  show,  what  they  were  designed  to  show,  that  the 


148  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

reason  for  swimming  toward  the  source  of  light  is  not  the  progression 
into  a  lighter  region.  But  they  do  not  indicate  in  the  least  that  the 
reactions  are  not  due  to  changes  in  intensity  of  illumination.  So  long 
as  turning  the  sensitive  anterior  end  away  from  the  source  of  light 
causes  a  greater  decrease  in  its  illumination  than  does  movement  into 
the  slightly  less  illuminated  region,  the  organism  will  move  toward  the 
source  of  light.  If  the  difference  in  intensity  of  light  in  different  parts 
of  the  drop  were  increased  till  the  change  in  illumination  due  to  pro- 
gression is  greater  than  the  change  due  to  swinging  the  anterior  end  away 
from  the  source  of  light,  then  the  positive  organisms  would  gather  in 
the  more  illuminated  regions.  This  is  the  condition  of  affairs  in  the 
experiment  shown  in  Fig.  98. 

In  the  swarm  spores,  as  in  Euglena,  the  positive  reaction  usually 
changes  to  a  negative  one  when  the  light  is  much  increased.  We  can 
thus  distinguish  an  optimum  intensity  of  light,  to  which  the  organisms 
may  be  said  to  be  attuned.  Either  increase  or  decrease  from  the  op- 
timum causes  the  avoiding  reaction.  Often  the  organisms  are  positive 
when  placed  at  some  distance  from  a  window,  but  become  negative 
when  brought  nearer.  There  is  much  variation  among  different  species, 
and  even  among  different  individuals  of  the  same  species,  as  to  the 
amount  of  light  that  causes  this  change  from  positive  to  negative.  Some- 
times, with  a  given  intensity  of  light,  half  the  individuals  of  Ulothrix 
are  found  to  be  positive,  the  other  half  negative  (Strasburger,  I.e.  p.  17). 
The  same  individual  is  seen  at  times  to  be  at  first  positive,  later  negative. 
Some  of  the  influences  which  modify  the  reaction  to  light  are  known. 
Certain  swarm  spores  are  attuned  to  a  stronger  light  in  the  early  stages 
of  development  than  in  the  later  stages.  Specimens  grown  in  shaded 
regions  seem  attuned  to  less  intense  light  than  those  living  in  well- 
lighted  cultures.  That  is,  the  organisms  are  attuned  more  nearly  to 
the  light  to  which  they  are  accustomed.  But  subjection  to  darkness 
sometimes  causes  negative  organisms  to  become  for  a  short  time  positive. 
Haematococcus  is  negative  in  a  certain  intensity  of  light,  gathering  at 
the  negative  side  of  the  drop.  Now  the  preparation  is  covered  and 
left  in  the  dark  for  a  few  minutes,  then  the  cover  is  removed.  At  once 
the  Haematococci  leave  the  negative  side  and  swim  toward  the  light 
for  a  short  distance.  But  this  lasts  only  a  moment.  After  reaching 
the  middle  of  the  drop,  they  swim  back  again  to  the  negative  side.  An 
increase  of  temperature  increases  the  tendency  to  a  positive  reaction  to 
strong  light ;  a  decrease  of  temperature  has  the  opposite  effect.  Lack 
of  oxygen  increases  the  tendency  to  a  positive  reaction.  This  is  ac- 
counted for  by  the  fact  that  the  green  organisms  produce  oxygen  in  the 
light. 


REACTIONS  OF  INFUSORIA  TO  LIGHT  AND  TO  GRAVITY    149 

A  change  in  the  intensity  of  light  does  not  as  a  rule  produce  its 
characteristic  effect  immediately,  but  requires  a  definite  interval  of  time. 
When  the  fight  is  faint  and  the  organisms  are  swimming  toward  it,  if 
the  light  is  suddenly  increased  to  an  intensity  to  which  they  are  nega- 
tive, the  swarm  spores  continue  to  swim  toward  it  for  some  time.  The 
interval  may  amount  to  as  much  as  half  a  minute.  At  the  end  of  this 
period  they  turn  and  swim  away  from  the  light.  Again,  when  the  or- 
ganisms are  swimming  away  from  a  strong  light,  a  sudden  decrease 
in  illumination  causes  them  to  become  positive  only  after  some  seconds. 
But  in  some  species  there  is  no  such  delay  in  the  effects  of  a  change  of 
illumination. 

To  sum  up,  we  find  that  the  reactions  to  light  occur  in  the  infusoria 
in  essentially  the  same  way  as  do  the  reactions  to  most  other  stimuli, 
through  the  avoiding  reaction  ;  that  is,  by  the  method  of  trying  movements 
in  different  directions.  The  cause  of  reaction  is  a  change  in  the  intensity 
of  light,  —  primarily  that  affecting  the  sensitive  anterior  end.  Changes 
in  intensity  may  be  produced  either  (1)  by  the  progression  of  the  or- 
ganism into  a  region  of  greater  or  less  illumination,  or  (2)  by  the  swinging 
of  the  sensitive  anterior  end  toward  or  away  from  the  source  of  light, 
so  that  it  is  shaded  at  one  moment  and  strongly  lighted  the  next.  Usually 
these  two  classes  of  changes  work  in  unison  ;  when  they  are  opposed,  the 
organism  reacts  in  accordance  with  that  which  is  stronger.  When  the 
second  class  of  changes  above  mentioned  is  the  determining  factor, 
the  organism  continues  to  react  by  trial  till  these  changes  cease.  This 
results  in  producing  orien'ation  with  anterior  end  directed  toward  or 
away  from  the  source  of  light.  In  strong  light  the  effect  of  an  increase 
or  decrease  of  intensity  is  often  the  reverse  of  that  observed  in  weak 
light. 


's1 


2.   Reaction  to  Gravity  and  to  Centrifugal  Force 

A  considerable  number  of  infusoria  have  been  found  to  react  to 
gravity  in  much  the  same  way  as  does  Paramecium  (Jensen,  1893). 
As  a  rule,  when  placed  in  vertical  tubes,  they  rise  to  the  upper  end. 
The  following  infusoria  have  been  found  to  behave  in  this  way :  Among 
the  flagellates:  Euglena,  Chlamydomonas,  Haematococcus,  Polytoma, 
Chromulina;  among  the  ciliates:  Paramecium  bursar  ia,  Urostyla. 
S pirostomum  ambiguum  takes  at  times  a  vertical  position  in  the  water 
a  short  distance  above  the  bottom,  with  anterior  end  upward.  Under 
these  circumstances  it  is  anchored  by  an  invisible  thread  of  mucus,  as 
may  be  observed  by  passing  a  glass  rod  between  it  and  the  bottom 
(Fig.  82).     The  stationary  position  oriented  with  reference  to  gravity 


150  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

seems  to  be  the  result  of  a  slight  activity  of  the  cilia,  tending  to  cause 
movement  upward,  combined  with  the  downward  pull  of  the  thread 
at  the  posterior  end.  Jensen  found  that  Colpoda  cucullus,  Colpidium 
col  pod  a,  Ophryoglena  flava,  and  Coleps  hirtus  showed  no  clear  reac- 
tion to  gravity. 

There  is  reason  to  suppose  that  reaction  to  gravity,  where  it  occurs, 
is  brought  about  in  the  same  manner  as  in  Paramecium.  The  details 
given  in  the  account  of  Paramecium  therefore  need  not  be  repeated  here. 

As  a  general  rule  the  reaction  to  gravity  is  easily  masked  by  reactions 
to  other  stimuli.  It  is  shown  in  a  marked  way  only  when  other  effective 
stimuli  are  largely  absent,  and  in  cases  of  conflict  with  other  reactions, 
it  is  usually  the  reaction  to  gravity  that  gives  way.  In  some  cases  the 
action  of  other  agents  causes  the  reaction  to  gravity  to  become  reversed, 
just  as  in  Paramecium.  Massart  (1891  a)  finds  that  this  effect  is  pro- 
duced in  Chromulina  by  lowering  the  temperature  to  5-7  degrees  C. 

A  number  of  infusoria  are  known  to  react  to  centrifugal  force  in  the 
same  way  as  to  gravity.  They  swim  in  the  opposite  direction  from 
that  in  which  the  centrifugal  force  tends  to  carry  them,  just  as  Parame- 
cium does.  It  is  probable  that  in  all  cases  centrifugal  force  could  be 
substituted  for  gravity  without  essential  alteration  of  the  reactions. 
Schwarz  (1884)  found  that  Euglena  and  Chlamydomonas  react  to  cen- 
trifugal force  when  it  is  equal  to  about  -|-  the  force  of  gravity,  and  con- 
tinues the  reaction  till  the  centrifugal  force  is  about  8^-  times  gravity. 
Above  this  they  are  passively  carried  in  the  direction  of  action  of  the 
centrifugal  force. 

LITERATURE  VIII 
Behavior  of  Infusoria  in  General 

A.  Reactions  to  light:  Jennings.  1904  a\  Strasburger.  1878;  Engelmann, 
1882;  Mast,  1906;  Famintzin,  1867;  Hertel,  1904;  Holt  and  Lee,  1901 ; 
Holmes,  1903;  Oltmanns,  1892. 

B.  Reactions  to  gravity :  Jensen,  1893;  Massart,  i 891  a ;  Schwarz,  1884. 


CHAPTER   IX 
REACTIONS   OF   INFUSORIA   TO   THE   ELECTRIC   CURRENT 

i.   Diverse  Reactions  of  Different  Species  of  Infusoria 

There  is  great  diversity  in  the  gross  features  of  the  behavior  of  differ- 
ent infusoria  under  the  action  of  the  continuous  electric  current.  Some 
swim,  like  Paramecium,  to  the  cathode ;  some  to  the  anode ;  some  take 
a  transverse  position ;  some  swim  to  one  electrode  in  a  weak  current, 
to  the  other  in  a  strong  current ;  some,  finally,  do  not  react  at  all.  Yet, 
in  spite  of  this  great  diversity,  we  find  the  fundamental  effect  of  the 
current  on  the  motor  organs  to  be  almost  identically  the  same  through- 
out the  series.  In  all  infusoria  having  cilia  in  different  regions  of  the 
body,  the  cilia  of  the  cathode  region  strike  forward,  those  of  the  anode 
region  backward,  just  as  we  have  seen  to  be  the  case  in  Paramecium. 
How  the  organisms  move  under  these  conditions  depends  on  the  pecu- 
liarities of  structure  and  of  the  action  system  of  the  infusorian  in  ques- 
tion. We  shall  review  here  the  different  types  of  behavior  under  the 
action  of  electricity,  endeavoring  to  show  how  each  is  brought  about. 

A.  Reaction  to  Induction  Shocks 

We  may  again  take  up,  first,  the  reactions  to  single  induction  shocks, 
studied  by  Roesle  (1902)  and  Statkewitsch  (1903).  In  all  infusoria 
investigated  the  reaction  to  moderately  strong  induction  shocks  is  es- 
sentially similar  to  the  reaction  to  other  stimuli.  The  animal  usually 
responds  to  the  shock  by  the  avoiding  reaction,  which  begins  with  a 
reversal  of  the  cilia  in  that  part  of  the  body  directed  toward  the  anode. 
In  some  cases,  however,  the  induction  shock  causes,  like  a  weak  mechani- 
cal stimulus,  a  mere  movement  forward  (Roesle,  1902).  If  the  shock 
is  a  powerful  one,  the  body  may  contract  in  the  anode  region,  or,  in  the 
case  of  very  contractile  species,  such  as  Lacrymaria  and  Spirostomum, 
the  entire  body  may  contract.  Reaction  takes  place  most  readily  as  a 
rule  when  the  sensitive  anterior  end  is  directed  toward  the  anode,  or 
especially,  according  to  Roesle,  when  the  mouth  opening  is  precisely 
directed  toward  the  anode.  When  the  animal  is  in  the  transverse  posi- 
tion, it  is  least  affected  by  the  induction  shock,  and  in  many  cases  it  is 

151 


!52 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


less  affected  when  the  aboral  side  is  directed  toward  the  anode,  than  in 
the  opposite  position. 

B.  Reaction  to  the  Constant  Current 

Under  the  action  of  the  constant  current  there  are  a  few  infusoria 
which  do  not  react  at  all,  so  far  as  known.  This  is  the  case,  for  example, 
with  Euglena  viridis.     Even  with  powerful  currents  it  shows  no  reaction. 

The  larger  number  of  free  ciliate  infusoria  swim  under  the  influence 
of  the  constant  current  to  the  cathode,  while  a  few  swim  to  the  anode 
or  take  a  transverse  position.  A  considerable  number  of  flagellates 
swim  to  the  anode,  though  some  swim  to  the  cathode. 

The  reaction  of  the  flagellates  has  been  little  studied  in  any  precise 
way.  Owing  to  their  minuteness  it  is  usually  very  difficult  to  deter- 
mine their  exact  movements.  According  to  Verworn  (1889  b),  Trache- 
lomonas  and  Peridinium  swim  to  the  cathode;  Polytomella  uvella, 
Cryptomonas  ovata,  and  Chilomonas  Paramecium  to  the  anode.  In 
stronger  currents  some  of  the  individuals  of  Chilomonas  swim  to  the 
cathode.  The  reason  for  the  diversity  in  the  reactions  of  different 
flagellates  has  not  been  determined.  In  the  case  of  Trachelomonas, 
according  to  Verworn,  the  flagellum  is  strongly  stimulated  when  directed 
toward  the  anode.  The  result  is  that  it  strikes  strongly  in  such  a  way 
as  to  turn  the  organism  around,  —  doubtless  by  a  typical  avoiding 
reaction  similar  to  that  described  on  page  in  for  Chilomonas.  On 
reaching  a  position  with  anterior  end  directed  to  the  cathode,  it  is  no 
longer  effectively  stimulated ;  it  therefore  continues  to  move  toward  the 
cathode.  In  Chilomonas  the  orientation  to  the  electric  current  is  known 
to  be  brought  about  through  the  typical  avoiding  reaction.  That  is, 
the  animal  turns  toward  the  smaller  lip  (Fig.  72,  y),  till  orientation  is 
attained  (Pearl,  1900).  Since  in  the  flagellates  the  motor  organs  are  all 
at  one  end,  all  bear  the  same  relation  to  cathode  or  anode,  so  that  we 
cannot  expect  any  opposition  in  the  action  of  the  different  flagella,  such 
as  we  find  in  the  cilia  of  different  regions  in  Paramecium.  There  is 
thus  no  sign  in  the  flagellates  of  that  lack  of  coordination  or  of  an 
apparent  attempt  to  move  in  two  directions  at  once,  which  we  find  in 
Paramecium. 

Among  the  Ciliata,  most  species,  under  usual  conditions,  turn  the 
anterior  end  to  the  cathode  and  move  toward  that  electrode.  But 
Opalina  moves,  usually,  to  the  anode,  and  Spirostomum  as  a  rule  takes 
a  transverse  position.  Certain  variations  in  the  reactions  under  different 
conditions  will  be  brought  out  later. 

Among  the  organisms  which  pass  to  the  cathode,  the  manner  in  which 


REACTIONS  OF   INFUSORIA    TO  ELECTRIC   CURRENT 


153 


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orientation  takes  place  varies  in  different  species.  The  direct  effect 
of  the  current  is,  as  in  Paramecium,  to  cause  the  cilia  on  the  cathode 
side  to  strike  forward,  while  those  on  the  anode  side  strike  backward. 
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itself,  in  turning  the  animals 
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many  species,  as  our  study 
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stimuli  has  shown  us,  there 
is  a  strong  tendency  to  turn 
toward  one  side  rather  than 
the  other,  usually  toward 
the  aboral  side,  —  that  oppo- 
site the  peristome.  The  cilia 
of  the  peristome  are  usually 
more  powerful  than  those  of 
the  remainder  of  the  body, 
so  that  the  direction  in  which 
the  animal  turns  depends 
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cilia  strike.  When  the  peris- 
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backward,  the  organism 
turns  toward  the  opposite  or 
aboral  side,  with  little  regard 
to  the  beat  of  the  remainder 
of  the  cilia.  These  peristo- 
mal cilia  are  as  a  rule  lim- 
ited to  one  of  the  four 
quarters  into  which  the  sur- 
face of  the  body  can  be  di- 
vided, as  illustrated  in  Fig. 
100.  They,  of  course,  beat 
backward  when  either  the 
end  bearing  them,  or  the  side 
bearing  them,  is  directed 
toward  the  anode  (1-3,  Fig. 
100),  so  that  in  these  positions  the  animal  turns  toward  the  aboral  side 
in  order  to  reach  the  position  of  orientation,  just  as  it  does  in  response 
to  other  stimuli.  It  is  only  when  the  side  bearing  the  peristome  is  di- 
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154 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


+ 


Fig.  ioi. — Transverse  (or  oblique)  posi- 
tion and  movement  of  Oxytricha  under  the 
action  of  the  electric  current,  when  the  animals 
are  in  contact  with  the  substratum.  The 
peristome  is  directed  toward  the  cathode. 


to  turn  the  organism  toward  the  oral  or  peristomal  side  (Fig.  ioo,  6). 
Under  these  circumstances,  another  principle  requires  consideration. 
Normally  the  peristomal  cilia  strike  backward.  When  they  strike  for- 
ward, they  develop  much  less  energy,  —  less  turning  power,  —  than  when 
they  strike  backward.  Therefore,  when  in  the  position  shown  at  6, 
Fig.  ioo,  the  turning  is  much  less  rapid  than  in  other  positions,  and  may 
easily  be  prevented  by  a  slight  resistance.  These  relations  will  be 
understood  by  an  examination  of  the  diagram  (Fig.  ioo). 

In  Paramecium,  as  we  have  seen,  the  same  condition  of  affairs  is 
exemplified  to  a  certain  degree,  so  that  the  organism  turns  toward  the 

oral  side  in  all  positions  save  from 
d  to  /,  Fig.  63.  In  the  Hypo- 
tricha  (Oxytricha  and  Stylo- 
nychia)  this  condition  is  most 
typically  exemplified.  A  large 
share  of  the  body  cilia  are  absent 
or  have  taken  the  function  of  legs, 
while  the  peristomal  cilia  are  very 
powerful.  In  almost  all  cases 
these  organisms  become  oriented 
to  the  electric  current  by  turning 
toward  the  aboral  (right)  side.  It  is  only  when  the  peristomal  cilia  are 
squarely  facing  the  cathode  (Fig.  100,  6)  that  the  animal  may  turn  toward 
the  oral  (left)  side.  In  this  position  the  peristomal  cilia  beat  forward, 
and  all  the  cilia  of  the  body  aid  in  turning  the  organism  toward  the  oral 
side.  On  reaching  a  position  with  anterior  end  directed  to  the  cathode  the 
peristomal  cilia  are  directed  forward,  but  their  beating  has  become  so  weak 
as  to  be  almost  without  effect.  The  animal,  therefore,  retains  this  position. 
When  specimens  of  the  Hypotricha  are  in  contact  with  a  surface,  as 
is  usually  the  case,  the  forward  beat  of  the  peristomal  cilia  is  often  so 
weak  and  ineffective  in  the  transverse  or  oblique  position  (Fig.  100,  6) 
that  it  does  not  turn  the  animal  against  the  resistance  offered  by  the 
attachment  of  the  ventral  cilia.  Such  specimens,  therefore,  remain  in 
the  transverse  or  oblique  position,  the  anterior  end  usually  slightly  in- 
clined toward  the  cathode,  as  in  Fig.  101.  In  this  position  they  run 
forward.  When  the  current  is  reversed,  so  that  the  anode  lies  next  the 
peristome,  the  powerful  peristomal  cilia  strike  backward.  The  ani- 
mals, therefore,  turn  toward  the  aboral  (right)  side  till  they  have  again 
become  nearly  transverse  to  the  current.  They  then  move  forward  in 
the  direction  so  indicated.  Similar  phenomena  are  at  times  to  be  ob- 
served in  other  ciliates,  not  belonging  to  the  Hypotricha.  This  is  true, 
as  we  have  seen,  even  for  Paramecium. 


REACTIONS   OF  INFUSORIA    TO   ELECTRIC   CURRENT 


155 


Fig.  102.  —  Diagrams  of  the  reaction  of  Colpidium  to  the  electric 
current  when  in  various  positions.  Based  on  the  descriptions  and 
figures  given  by  Pearl  (1900). 


Thus  we  can  distinguish  two  factors  in  the  turning  produced  by  the 
electric  current.  The  first  is  a  tendency  to  turn  directly  toward  the 
cathode,  the  second  a  tendency  to  turn  toward  a  structurally  defined 
side,  —  usually  the  aboral  side.  The  conflict  of  these  tendencies  when 
the   animal  is    in  b  c 

certain    positions,  a  ,^  ^*<4,''^*°       '--^      d 

and  their  mutual 
reenforcement  in 
other  positions, 
often  give  rise  to 
peculiar  and  com- 
plicated phenom- 
ena. Thus,  in  Colpidium,  as  described  by  Pearl  (1900),  we  have  the 
following  different  methods  of  reacting  to  the  electric  current.  (It 
should  be  premised  that  Colpidium  tends  under  ordinary  conditions  to 
turn  toward  the  aboral  side.) 

(1)  When  the  anterior  end  is  directed  approximately  toward  the 
anode,  or  in  any  position  in  which  the  aboral  side  is  nearest  the  cathode, 

Colpidium  turns  toward  the 
aboral  side  (Fig.  102,  a,  b),  till 
the  anterior  end  is  directed 
toward  the  cathode.  Both  the 
factors  mentioned  above  coop- 
erate to  produce  this  result. 

(2)  When  the  animal  is 
nearly  transverse,  or  is  ob- 
lique, with  the  oral  side  next 
to  the  cathode,  it  usually 
swims  slowly  forward,  and  at 

>lpid  1  reacts  to  the  electric  current  when  transverse  the  Same  time  gradually  turns 
with  the  oral  side  to  the  cathode.  Constructed  from  toward  the  OYO.I  side  till  it  be- 
data  given  bv  Pearl  (iqoo).  •       ,     i    /-rp-  „    j\ 

6         -  vy  comes  oriented  (rig.  102,  c-a). 

The  two  tendencies  mentioned  above  oppose  each  other  in  this  case,  and 
the  first  one  overcomes  the  second. 

(3)  But  in  other  cases  when  the  animal  is  in  the  position  described 
in  the  last  paragraph  (Fig.  103,  a)  it  reacts  in  another  way.  It  moves 
forward,  slowly  turning  toward  the  oral  side  (Fig.  103,  a-b),  then  turns 
on  its  long  axis  (b-c)  (as  happens  in  ordinary  locomotion).  This  brings 
the  aboral  side  next  to  the  cathode  (c).  Now  the  animal  turns  suddenly 
toward  the  aboral  side  till  the  anterior  end  is  directed  toward  the  cathode 
(Fig.  103,  d).  In  this  case,  then,  the  two  tendencies  mentioned  above 
oppose  each  other  till  the  revolution  on  the  long  axis  occurs,  then  they 
reenforce  each  other. 


Fig.    103.  —  Diagram   of  one   method   by    which 


i56 


BEHAVIOR   OF    THE   LOWER   ORGANISMS 


(4)   If  Colpidium  is  squarely  transverse,  with  oral  side  to  the  cathode 
(Fig.  104,  1),  or  especially  if  the  anterior  end  is  a  little  inclined  toward 

the  anode,  the  organism  often  starts  trans- 
versely to  the  current.  Suddenly  it  jerks  its 
body  a  little  toward  the  aboral  side  (Fig. 
104,1-2),  then  moves  forward  again.  Again  it 
jerks  toward  the  aboral  side  (3),  again  moves 
forward,  and  repeats  this  behavior  until  the 
anterior  end  is  directed  toward  the  anode. 
Then  it  turns  steadily  toward  the  aboral  side 
till  the  anterior  end  is  directed  toward  the 
cathode  (Fig.  104,  4-5).  In  this  behavior  the 
two  tendencies  mentioned  oppose  each  other, 
as  in  case  2,  but  the  second  one  prevails  over 
the  first. 

Various  combinations  of  these  different 
reaction  types  may  occur,  making  the  be- 
havior of  Colpidium  under  the  electric  cur- 
rent very  complicated.     Similarly  varied  be- 


0  — 


Fig.  104.  —  Another  method 

of  reaction  to  the  electric  current   havior  is  often  observed  in  other  infusoria, 

in    Colpidium.      After    Pearl  through  the  action  of  similar  causes. 
(1900). 

as 


In  such 


+ 


infusoria  as  Stentor,  where  the 
peristomal  cilia  form  a  circle  surrounding  the  anterior  end,  there  is  no 
reason  for  such  a  conflict  of  tendencies.  The  peristomal  cilia  are 
divided  by  an  electric  current  coming  from  one  side,  so  that  the  ani- 
mal turns  directly  away  from  the  side  on  which  these 
cilia  strike  backward  (Fig.  105).  If  the  anterior  end 
is  directed  toward  the  anode  at  the  beginning,  the 
animal  doubtless  turns  as  usual  toward  the  right 
aboral  side.  In  other  positions  the  usual  method  of 
turning  seems  to  have  no  effect  on  the  reactions.  In 
Vorticella  and  other  infusorians  resembling  Stentor 
in  the  distribution  of  the  cilia,  the  orientation  to  the 
current  would  doubtless  take  place  in  the  same  direct 
manner,  though  this  has  never  been  determined. 

In  Spirostomum  and  Opalina,  the  conflict  of  the 
two  tendencies  mentioned  above  leads  to  certain  very 
remarkable  and  complex  results.  Under  usual  con- 
ditions Spirostomum  takes  a  transverse  position  in 
the  electric  current,  while  Opalina  swims  to  the 
anode.  The  gross  features  of  the  behavior  thus  differ 
markedly  from  those  shown  by  most  other  infusoria. 


Fig.  105.  —  Re- 
action of  Stentor  when 
transverse  to  the  cur- 
rent. It  turns  directly 
toward  the  cathode, 
all  the  cilia  concur- 
ring to  produce  this 
effect. 


REACTIONS   OF  INFUSORIA    TO   ELECTRIC   CURRENT 


157 


But  Wallengren  has  shown  that  the  effect  of  the  current  is  in  these  in- 
fusoria of  essentially  the  same  character  as  in  others.  Let  us  examine 
briefly  the  facts  as  set  forth  by  Wallengren  (1902  and  1903). 

Spirostomum  (Fig.  106)  is  a  very  long,  slender  infusorian,  easily 
bent  in  any  direction,  and  very  contractile.  The  peristomal  cilia  are 
very  large  and  numerous,  extending  from  the  anterior  end  along  one 
side  to  a  point  behind  the  middle.  Whether  striking  forward  or  back- 
ward, the  beating  of  these  A 
cilia  is  decidedlv  more  effec-  / 
tive  than  that  of  the  cilia  on 
the  opposite  side  of  the 
body.  It  is  to  this  fact, 
taken  in  connection  with  the 
slenderness  and  suppleness 
of  the  body,  that  most  of 
the  peculiarities  in  the  reac- 
tion of  Spirostomum  to  the 
electric  current  are  due. 

In  a  very  weak  current, 
such  as  does  not  cause  con- 
traction of  the  body,  Spiro- 
stomum swims  to  the  cath- 
ode. The  cilia  on  the 
anodic  part  of  the  body 
strike  backward,  those  in 
the  cathodic  region  forward, 
just  as  happens  in  Para- 
mecium.     As    a    result,  the 

animal  takes  a  position  with  Fig.    106.   •   ■   Diagrams    illustrating     reaction     of 

anterior    end    directed  to   the   Spirostomum   to   the  electric  current.      A,  B,    D,    and 

E  after  Wallengren  (1903). 

cathode,    in    essentially    the 

same  manner  as  does  Paramecium,  —  usually  turning  to  the  aboral  side, 
but  in  certain  cases  toward  the  oral  side.  When  the  anterior  end  is 
directed  toward  the  cathode,  the  cilia  on  the  cathodic  half  of  the  body 
are  partly  directed  forward,  but  with  the  weak  current  most  of  them  still 
strike  most  strongly  backward.  Those  of  the  anode  half  of  course 
strike  backward,  so  that  the  general  result  is  to  drive  the  animal 
forward  to  the  cathode.  Sometimes  Spirostomum  under  these  condi- 
tions comes  against  the  bottom  or  other  solid  object ;  it  may  then  nearly 
or  quite  cease  to  move  forward.  The  facts  thus  far  are  quite  parallel 
to  those  observed  in  Paramecium. 

As  the  electric  current  is  made  stronger,  the  cilia  on  the  cathodic 


158  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

half  of  the  body  strike  more  powerfully  forward,  and  at  a  certain  strength 
their  effect,  tending  to  drive  the  animal  backward,  becomes  about  equal 
to  that  of  the  anodic  cilia,  tending  to  drive  it  forward.  The  result  is 
that  the  animals  move  neither  forward  nor  backward,  or  only  very 
slowly  in  one  direction  or  the  other.  They  thus  sink  to  the  bottom 
before  much  progress  has  been  made.  Now,  if  in  this  position  the  an- 
terior end  is  directed  toward  the  cathode  (Fig.  106,  A),  of  course  the 
cilia  of  the  anterior  (cathodic)  half  of  the  body  tend  to  push  the  animal 
backward,  while  those  of  the  opposite  half  tend  to  push  it  forward.  This 
push  in  opposite  directions  bends  the  supple  body  near  its  middle.  More- 
over, in  the  cathodic  half  the  peristomal  cilia  have  a  more  powerful  for- 
ward stroke  than  do  the  ordinary  cilia  on  the  opposite  side,  hence  the 
anterior  half  of  the  body  tends  to  bend  toward  the  peristomal  or  oral 
side.  The  general  result  is  that  the  animal  is  bent  into  the  position 
shown  in  Fig.  106,  B.  The  bending  of  the  anterior  part  of  the  body 
toward  the  oral  side  continues,  until  this  part  of  the  body  becomes  trans- 
verse to  the  current  (Fig.  106,  C).  The  body  may  now  become  com- 
pletely straightened  (Fig.  106,  D),  or  it  may  not.  But  in  either  case 
the  peristome  is  now  turned  toward  the  anode.  The  powerful  peris- 
tomal cilia  therefore  strike  backward,  causing  the  anterior  end  to  swing 
toward  the  aboral  side,  directing  it  again  toward  the  cathode,  as  indi- 
cated by  the  arrow  in  D.  On  becoming  directed  toward  the  cathode, 
the  original  condition  (Fig.  106,  A)  is  restored.  The  animal  therefore 
again  takes  the  positions  B,  C,  and  D.  It  thus  continues  to  squirm 
from  side  to  side.  But  during  its  movements  Spirostomum,  like  Para- 
mecium, frequently  revolves  on  its  long  axis.  This  often  happens  when 
in  the  position  shown  in  Fig.  106,  C,  so  that  the  animal  becomes  placed 
transversely  to  the  current,  with  peristome  to  the  cathode  (Fig.  106,  E). 
In  this  position  the  peristomal  cilia  are  directed  forward  and  have  there- 
fore comparatively  little  motor  effect.  If  at  the  same  time  the  animal 
comes  in  contact  with  the  bottom,  the  contact  reaction  may  overcome 
for  a  time  this  slight  motor  effect,  so  that  the  animal  lies  nearly  quiet, 
in  the  transverse  position.  If  now  the  current  is  reversed,  so  that  the 
peristome  is  at  the  anode  (Fig.  106,  D),  the  animal  at  once  swings  again 
toward  the  aboral  side.  Even  if  the  current  is  not  reversed,  the  animal 
usually  does  not  remain  long  in  the  position  shown  at  E.  The  peri- 
stomal cilia  being  more  effective  than  the  opposing  ones,  gradually  swing 
the  anterior  half  toward  the  oral  side.  Soon  a  bending  takes  place 
again,  as  in  B,  and  the  organism  is  forced  to  squirm  about  from  side 
to  side,  as  before. 

Thus  Spirostomum  finds  in  a  strong  current  no  position  of  equilib- 
rium, because  the  peristomal  cilia  have  always  a  more  powerful  effect 


REACTIONS   OF  INFUSORIA    TO  ELECTRIC   CURRENT  159 

than  the  opposing  ones,  and  because  the  opposed  action  of  the  cilia  on 
the  anodic  and  cathodic  halves  of  the  body  soon  bends  the  slender  body. 
It  thus  squirms  about  from  one  side  of  the  transverse  position  to  the 
other,  taking  many  shapes  besides  those  figured.  It  remains  quiet  only 
for  certain  periods  in  the  transverse  position  with  peristome  to  the  cath- 
ode, when  it  is  in  contact  with  a  surface:  this  is  a  result  of  the  inter- 
ference of  the  contact  reaction  with  the  reaction  to  the  electric  current. 
Under  the  action  of  the  current  alone,  the  reaction  of  Spirostomum  does 
not  tend  to  bring  it  to  a  position  where  it  is  not  effectively  stimulated, 
for  no  such  position  exists.  In  this  respect  the  electric  stimulus  shows 
again  a  marked  contrast  with  other  stimuli. 

In  Opalina  ranariim  the  first  marked  effect  of  the  electric  current  is 
to  cause  the  animals  to  swim  to  the  anode  instead  of  to  the  cathode. 
Its  reaction  seems  thus  in  striking  contrast  with  that  of  other  ciliate 
infusoria.  We  must  examine  the  reaction  in  Opalina,  following  Wallen- 
gren  (1902),  to  see  how  this  result  is  brought  about. 

Opalina  is  a  large,  flat,  disk-shaped,  parasitic  infusorian,  living  in 
the  large  intestine  of  the  frog.  For  experimental  work  it  is  examined 
in  physiological  salt  solution,  as  it  soon  dies  in  water.  There  is  no 
mouth,  since  food  is  obtained  by  absorption  over  the  entire  body  sur- 
face. The  body  is  closely  set  with  fine  cilia.  The  anterior  end  of  the 
body  is  more  pointed  than  the  posterior.  From  the  anterior  portion 
there  extends  backward  at  one  edge  a  convex  region,  ending  at  a  sort 
of  notch  in  the  middle  of  the  body  (Fig.  107,  x).  This  convex  region 
is  set  with  cilia  having,  as  we  shall  see,  a  somewhat  different  function 
from  those  of  the  remainder  of  the  body.  The  side  bearing  this  con- 
vexity is  usually  known  as  the  right  side. 

Opalina  swims  with  anterior  end  in  front,  at  the  same  time  usually 
revolving  on  its  long  axis.  When  stimulated  by  contact  with  a  solid, 
or  in  other  ways,  it  turns  toward  the  side  bearing  the  convexity  —  the 
right  side.  Observation  shows  that  this  movement  is  due  to  the  fact 
that  the  cilia  on  the  convexity  of  the  right  side  now  strike  forward  in- 
stead of  backward,  thus  necessarily  turning  the  animal  toward  the  side 
bearing  them.  In  this  way  the  typical  avoiding  reaction  of  Opalina  is 
produced. 

If  a  preparation  of  Opalina  in  physiological  salt  solution  is  sub- 
jected to  the  action  of  a  weak  electric  current,  the  animals  swim  to  the 
anode.  Examining  the  individuals,  it  is  found  that  the  cilia  on  the 
anode  half  of  the  body  strike  backward,  those  on  the  cathode  half  for- 
ward, exactly  as  in  Paramecium.  Why  then  does  Opalina  swim  to  the 
anode  instead  of  to  the  cathode? 

The  secret  of  this  difference  lies  in  the  following  facts.     The  cilia 


i6o 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


of  the  convexity  of  the  right  side  (Fig.  107,  x)  are  very  easily  reversed 
by  a  weak  current.  The  cilia  of  the  opposite  side,  on  the  other  hand, 
are  little  affected  by  a  weak  current.  Their  usual  backward  stroke  is 
decreased  in  power,  and  doubtless  some  of  the  cilia  are  reversed,  but  the 
general  effect  of  their  action  is  still  to  drive  the  animal  forward.  Let 
us  suppose  that  the  Opalina  is  at  first  transverse  to  the  electric  current, 
with  right  side  to  the  cathode,  as  in  Fig.  107,  1.     As  soon  as  the  current 


Fig.  107.  —  Diagrams  of  the  movements  of  the  cilia,  and  of  the  direction  of  turning,  in  the 
reaction  of  Opalina  to  the  electric  current.     After  Wallengren  (1902). 

begins  to  act,  the  cilia  of  the  right  (cathodic)  side  become  directed  for- 
ward, while  those  of  the  left  (anodic)  side  remain  directed  backward. 
The  result  is  of  course  to  turn  the  animal  to  the  right,  toward  the  cath- 
ode. Thus  the  specimen  passes  through  the  position  shown  in  Fig. 
107,  2,  and  comes  into  a  position  with  the  anterior  end  directed  toward 
the  cathode  (3).  The  cilia  of  the  anterior  part  of  the  body  are  now 
directed  partly  forward,  those  of  the  posterior  half  backward.  In  this 
position,  as  we  know,  Paramecium  remains ;  indeed,  the  whole  reaction 
thus  far  is  essentially  like  that  of  Paramecium.     But  in  Opalina,  so  long 


REACTIONS  OF    INFUSORIA    TO  ELECTRIC  CURRENT  161 

as  the  current  is  weak,  only  the  cilia  on  the  convexity  of  the  right  side 
strike  powerfully  with  their  reversed  stroke,  —  these  being  the  cilia  that 
are  reversed  in  the  usual  avoiding  reaction.  The  other  reversed  cilia 
strike  only  weakly.  In  consequence  the  animal  must  turn  toward  the 
right  side,  reaching  the  position  shown  in  Fig.  107,  4.  Here  most  of 
the  strong  cilia  x  of  the  convexity  are  still  striking  forward,  hence  the  ani- 
mal still  turns  toward  the  right.  A  little  beyond  4, — between  this  and 
5,  —  the  animal  reaches  a  position  where  the  tendencies  to  turn  in  oppo- 
site directions  are  equal.1  But  the  turning  which  has  been  initiated  in 
positions  1-4,  as  a  rule  has  given  the  animal  sufficient  momentum  to 
carry  it  past  this  dead  point,  so  that  it  reaches  the  anode  pointing  posi- 
tion (Fig.  107,  7).  Here  the  cilia  of  both  sides  of  the  anterior  end  are 
directed  backward.  When  striking  backward  the  cilia  x  of  the  convexity 
are  no  more  powerful  than  those  of  the  opposite  side.  Hence  there  is 
now  no  tendency  to  turn  farther,  and  the  anode-pointing  position  is 
retained.  Since  the  backward  stroke  of  the  anterior  cilia  is  more  power- 
ful than  the  forward  stroke  of  the  reversed  posterior  cilia,  the  animal  is 
carried  forward  to  the  anode.  Thus  in  a  weak  current  the  position  with 
anterior  end  directed  to  the  anode  is  the  stable  one,  so  that  in  the  course 
of  time,  after  some  oscillation,  the  animals  reach  this  position  and  swim 
toward  the  anode. 

Now  if  the  current  is  considerably  increased  in  strength,  the  cathodic 
cilia  are  caused  to  strike  more  strongly  forward  than  before.  Their 
motor  effect  therefore  nearly  equals  that  of  the  anodic  cilia,  so  that  the 
forward  movement  toward  the  anode  is  made  much  slower.  If  at  the 
time  the  current  is  made  the  Opalina  is  in  an  oblique  position,  as  will 
usually  be  the  case,  or  if  as  a  reaction  to  other  stimuli  during  the  passage 
of  the  current  it  passes  out  of  the  position  with  anterior  end  to  the  anode, 
then  another  effect  is  produced.  Suppose  it  comes  thus  into  the  position 
shown  in  Fig.  107,  8.  Then  the  larger  number  of  cilia  tend  to  turn  it  to 
the  right,  as  is  shown  by  the  arrows  at  8.  It  thus  comes  into  position  1, 
where  all  the  cilia  assist  in  turning  it  to  the  right ;  it  continues  in  the 
same  way  through  position  2  to  position  3,  with  anterior  end  pointing 
to  the  cathode.  With  a  weak  current,  as  we  have  seen,  this  position 
is  not  a  stable  one;  the  stronger  forward  beating  of  the  cilia  on  the 
convexity  of  the  right  side  cause  the  animal  to  continue  to  turn  to  the 
right.  But  with  a  stronger  current  this  becomes  changed.  Since  even 
in  a  weak  current  the  cilia  of  this  convexity  strike  as  strongly  forward 
as  they  can,  their  forward  stroke  is  not  increased  when  the  current  is 

1  If  the  animal  at  this  point  or  earlier  turns  on  its  long  axis,  as  it  frequently  does  in  its 
usual  locomotion,  it  must  now  swing  back  through  the  cathode-pointing  position,  till  it 
again  reaches  a  position  corresponding  to  4  or  5. 
M 


1 62  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

made  stronger.  But  as  the  current  is  increased,  the  forward  stroke  of 
the  cilia  on  the  left  side  of  the  anterior  half  of  the  body  becomes  more 
powerful,  —  just  as  happens  with  all  the  anterior  cilia  in  Paramecium. 
Hence,  when  the  current  reaches  a  certain  strength,  the  cilia  of  the  left 
side,  in  an  Opalina  pointing  toward  the  cathode,  beat  as  strongly  for- 
ward as  do  those  of  the  right  side.  There  is  then  no  cause  for  turning 
toward  either  the  right  or  the  left.  The  position  with  anterior  end 
directed  toward  the  cathode  has  become  a  stable  one.  Thus,  when  a 
strong  current  is  passed  through  a  preparation  of  Opalinas,  most  of  them 
become  directed  after  a  time  toward  the  cathode,  and  swim  slowly  in  that 
direction.  A  number  may  be  at  first  directed  toward  the  anode,  but  as 
soon  as  these  by  any  chance  get  out  of  the  anode-pointing  position,  they 
also  become  directed  toward  the  cathode. 

With  a  still  more  powerful  current  the  Opalinas  retain  nearly  or 
quite  the  position  with  anterior  end  to  the  cathode,  but  move  backward 
(or  sometimes  sideways)  toward  the  anode.  Wallengren  believes  that 
this  is  a  passive  movement  due  to  the  cataphoric  action  of  the  electric 
current.  In  Paramecium,  as  we  have  seen,  there  is  a  similar  move- 
ment under  these  conditions,  but  due  to  the  fact  that  the  cathodic  cilia 
beat  more  effectively  forward  than  do  the  anodic  cilia  backward. 

Thus  altogether  we  find  that  in  Opalina  the  electric  current  acts  on 
the  motor  organs  in  fundamentally  the  same  way  as  in  Paramecium. 
But  owing  to  peculiarities  of  the  action  system  of  Opalina,  this  results, 
with  a  weak  current,  in  movement  forward  toward  the  anode;  with  a 
stronger  current  in  movement  forward  toward  the  cathode;  with  a  still 
stronger  current  in  movement  backward  or  sideways  toward  the  anode. 

2.    Summary 

Reviewing  our  results  as  to  the  effect  of  the  continuous  electric  cur- 
rent on  the  ciliate  infusoria,  we  find  a  complete  agreement  throughout 
in  the  action  of  the  current  on  the  motor  organs,  with  the  greatest  pos- 
sible diversity  in  the  resulting  movements  of  the  animals.  In  all  cases 
the  cilia  in  the  anode  region  strike  backward,  as  in  the  normal  forward 
movement,  while  the  cilia  of  the  cathode  region  are  reversed,  striking 
forward.  With  different  strengths  of  current,  and  with  infusoria  of 
different  action  systems,  this  results  sometimes  in  movement  forward  to 
the  cathode ;  sometimes  in  movement  forward  to  the  anode ;  sometimes 
in  a  cessation  of  movement,  the  anterior  end  continuing  to  point  to  the 
cathode ;  sometimes  in  a  backward  movement  to  the  anode ;  sometimes 
in  a  position  transverse  to  the  current,  the  animal  either  remaining  at 
rest  or  moving  across  the  current.     These  variations  depend  upon  the 


REACTIONS   OF  INFUSORIA    TO   ELECTRIC   CURRENT  163 


differences  in  the  strength  of  beat  of  the  cilia  of  different  regions  of  the 
body  under  currents  of  different  strength.  The  different  effects  pro- 
duced may  be  classified,  as  to  their  causes,  in  the  following  way:  — 

1.  The  orientation  with  anterior  end  to  the  cathode  is  due  to  the 
fact  that  the  cilia  of  the  cathodic  side  strike  forward ;  of  the  anodic  side 
backward.  This  may  be  assisted  or  hindered  by  the  usual  tendency  of 
the  organisms  to  turn  when  stimulated  toward  a  certain  structurally 
defined  side. 

2.  The  movement  toward  the  cathode  in  weak  or  moderate  currents 
is  due  to  the  fact  that  under  these  conditions  the  backward  stroke 
of  the  anodic  cilia  is  more  powerful  than  the  forward  stroke  of  the 
cathodic  cilia. 

3.  The  cessation  of  progression  in  a  stronger  current,  with  reten- 
tion of  the  cathode-pointing  orientation,  is  due  to  the  fact  that  as  the 
current  is  increased  the  forward  stroke  of  the  cathodic  cilia  becomes 
more  powerful,  till  it  equals  the  backward  stroke  of  the  anodic  cilia. 

4.  The  swimming  backward  toward  the  anode  in  a  still  stronger  cur- 
rent is  due  to  a  continued  increase  in  the  power  of  the  forward  stroke  of 
the  cathodic  cilia,  so  that  they  overcome  the  tendency  of  the  anodic  cilia 
to  drive  the  animal  forward.  (In  Opalina,  Wallengren  believes  that  this 
backward  movement  is  due,  at  least  partly,  to  the  cataphoric  effect  of 
the  current.) 

5.  The  unstable  transverse  position  seen  in  some  cases  (Spiro- 
stomum)  is  due  primarily  to  the  fact  that  the  cilia  of  one  side  of  the 
elongated  body  are  more  powerful,  when  striking  either  backward  or 
forward,  than  are  the  corresponding  cilia  of  the  opposite  side.  As  a 
result,  neither  the  position  with  anterior  end  to  the  cathode  nor  that 
with  anterior  end  to  the  anode  is  a  stable  one,  and  the  animal  is  com- 
pelled to  oscillate  about  a  transverse  position.  This  result  is  accen- 
tuated by  the  slenderness  and  suppleness  of  the  body  in  these  species. 

6.  The  orientation  with  anterior  end  to  the  anode  seen  in  certain 
cases  (Opalina  in  a  weak  current)  is  due  to  the  fact  that  the  cilia  of  one 
side  of  the  anterior  half  of  the  body  are  more  readily  reversed  than  the 
opposing  cilia,  and  their  reversed  stroke  is  more  powerful,  though  their 
usual  backward  stroke  is  not.  The  result  is  that  the  position  with  an- 
terior end  to  the  cathode  becomes  unstable,  while  the  position  with 
anterior  end  to  the  anode  is  stable  so  long  as  accidental  causes  do  not 
produce  slight  deviations  from  it. 

7.  The  transverse  or  oblique  position,  at  rest  or  with  movement 
athwart  the  current,  is  due  to  interference  between  the  contact  reaction 
and  the  effect  of  the  current.  This  position  is  maintained  only  when 
the  more  powerful  cilia  of  the  peristome  are  striking  forward ;   that  is, 


1 64  BEHAVIOR  OF   THE   LOWER   ORGANISMS 

when  the  peristome  is  directed  toward  the  cathode.  When  the  peri- 
stomal cilia  are  thus  striking  forward,  their  action  is  comparatively  in- 
effective, so  that  it  does  not  overcome  the  attachment  to  the  substratum, 
in  the  contact  reaction. 

3.    Theories  of  the  Reaction  to  Electricity 

What  is  the  cause  of  the  reaction  to  the  electric  current  ?  The  most 
striking  phenomenon  in  a  general  view  is  usually  a  movement  of  the 
organisms  en  masse  toward  the  cathode  or  anode.  It  is  well  known  that 
the  electric  current  has  the  property  of  carrying  small  bodies  suspended 
in  a  fluid  toward  the  cathode  or  anode,  depending  on  the  conditions. 
This  phenomenon  is  commonly  known  as  cataphoric  action,  or  as  elec- 
trical convection.  When  the  movement  of  small  organisms  toward  one 
of  the  electrodes  is  mentioned,  the  first  thought  that  comes  to  mind  is 
of  course  the  possibility  that  they  are  thus  passively  carried  by  the  cata- 
phoric action  of  the  current.  But  this  view  can  be  maintained  only  on 
the  basis  of  an  extraordinarily  superficial  acquaintance  with  the  facts. 
Careful  study  shows,  as  we  have  seen,  that  the  current  has  definite  and 
striking  effects  on  the  cilia,  and  that  it  is  to  these  effects  that  the  peculiari- 
ties of  movement  under  the  action  of  the  current  are  due.  Nevertheless, 
the  theory  that  the  phenomena  are  passive  movements  due  to  the  cata- 
phoric action  of  the  current  continues  to  be  brought  gravely  forward  at 
intervals,  and  doubtless  this  will  continue.  The  fundamental  fallacy 
of  this  theory  is  the  idea  that  we  must  account  in  some  way  by  the  action 
of  the  current  for  the  fact  that  the  organisms  move.  This  is  quite  un- 
necessary, for  they  move  equally  without  the  action  of  the  current.  The 
movement  is  spontaneous,  so  far  as  the  electric  current  is  concerned.  It 
takes  place  by  the  agency  of  the  motor  organs  of  the  animal,  driven  by 
internal  energy,  and  acting  upon  the  resistance  furnished  by  the  water. 
It  is  only  the  changed  direction  of  the  movement  that  the  electric  cur- 
rent must  account  for.  There  is  no  place  for  the  agency  of  the  cata- 
phoric action  in  transporting  the  animals,  for  they  are  visibly  transport- 
ing themselves,  just  as  they  were  before  the  cataphoric  action  began. 
It  is  absolutely  clear  that  the  movements  of  the  cilia,  described  in  the 
preceding  pages,  are  at  the  bottom  of  the  observed  behavior,  and  any 
explanation  of  the  reaction  to  electricity  must  account  for  the  influence 
of  this  agent  on  the  cilia.  This  the  theories  of  passive  movement  by 
cataphoric  action  make  no  attempt  to  do. 

The  clearest  disproof  of  the  theory  that  the  movement  is  a  passive 
one  due  to  cataphoresis  is  of  course  the  well-established  positive  proof 
that  the  movement  is  an  active  reaction  of  the  organism.     But  the  theory 


REACTIONS   OF  INFUSORIA    TO   ELECTRIC   CURRENT  165 

can  be  disproved  on  other  grounds.  Statkewitsch  (1903  a)  shows  that 
dead  or  stupefied  Paramecia  that  are  suspended  in  viscous  fluids  are  not 
moved  by  cataphoric  action,  while  living  Paramecia  in  the  same  fluids 
swim  to  the  cathode.  Dead  or  stupefied  Paramecia  placed  in  water  in 
a  perpendicular  tube  through  which  an  electric  current  is  passed  sink 
slowly  and  steadily  to  the  bottom,  whatever  the  direction  of  the  current, 
while  living  specimens  pass  upward  when  the  cathode  is  above.  If  the 
anode  is  above  and  a  very  strong  current  is  used,  the  living  animals  swim 
backward  to  the  anode,  as  described  on  page  98.  They  therefore  move 
upward  against  gravity,  while  dead  or  stupefied  specimens  with  the  same 
current  sink  slowly  to  the  bottom  of  the  tube.  It  is  thus  clear  that  neither 
the  forward  movement  to  the  cathode  nor  the  backward  movement 
toward  the  anode  is  directly  due  to  the  cataphoric  action  of  the  current, 
for  this  action  is  not  capable  of  producing  the  observed  movements. 

The  cataphoresis  might  of  course  act  in  some  way  as  a  stimulus  to 
induce  the  observed  active  movements  of  the  cilia.  This  is  apparently 
the  view  toward  which  Carlgren  (1899,  1905  a)  and  Pearl  (1900)  are 
inclined.  This  is  of  course  a  theory  of  a  radically  different  character 
from  that  which  we  have  been  considering.  Just  how  this  effect  would 
be  produced  through  the  known  physical  action  of  the  current  has  not 
been  shown. 

Coehn  and  Barratt  (1905)  hold  that  Paramecia  in  ordinary  water 
become  positively  charged,  through  the  escape  into  the  water  of  the 
negative  ions  of  the  electrolytes  which  the  body  holds,  while  the  positive 
ions  are  retained.  As  a  result  of  this  positive  charge,  the  electric  cur- 
rent tends  to  carry  the  animals  to  the  cathode;  the  infusoria  are  held 
to  follow  this  tendency  and  swim  with  the  pull  of  the  current  toward  the 
cathode.  In  a  solution  containing  more  electrolytes,  it  is  held  that  the 
positive  ions  escape  from  the  protoplasm;  hence  the  animals  become 
negatively  charged.  They  therefore  pass  to  the  anode  when  placed  in 
a  solution  of  sodium  chloride  or  sodium  carbonate.  This  theory  leaves 
unaccounted  for  precisely  the  essential  feature  of  the  reactions,  —  the 
cathodic  reversal  of  the  cilia.  It  likewise  fails  to  account  for  the  fact 
that  as  the  current  becomes  stronger  the  passage  to  the  cathode  ceases 
and  the  animals  begin  to  swim  backward  to  the  anode,  and  for  the 
further  fact  that  individuals  which  have  become  accustomed  to  a  solu- 
tion of  sodium  chloride  or  carbonate  no  longer  swim  to  the  anode,  but 
pass  to  the  cathode  as  usual.  These  facts  appear  to  be  absolutely  fatal 
to  the  view  under  consideration.  Little  is  to  be  hoped  of  any  theory 
that  neglects  what  is  clearly  the  fundamental  phenomenon  in  these 
reactions,  —  the  cathodic  reversal  of  the  cilia. 

Another  theory  has  held  that  the  reaction  to  the  electric  current  is 


+ 


1 66  BEHAVIOR   OF   THE   LOWER  ORGANISMS 

due  to  the  electrolytic  effect  of  the  current  on  the  fluid  containing  the 
animals  (Loeb  and  Budgett,  1897).  The  water  of  course  contains  elec- 
trolytes. These  are  separated  by  the  current  into  their  component  ions, 
and  the  products  of  this  electrolysis  may  be  deposited  on  opposite  poles 
of  a  body  immersed  in  the  fluid.  There  is  some  reason  to  suppose  that 
an  alkali  may  be  deposited  on  that  portion  of  the  surface  of  the  infusorian 
where  the  current  is  entering  its  protoplasm  (the  anodic  surface),  an 
acid  where  it  is  leaving  the  protoplasm  (the  cathodic  surface).  The 
relative  amount  of  such  action  is  unknown,  but  the  suggestion  is  made 
that  the  observed  effects  of  the  current  are  due  to  these  chemicals.  This 
very  interesting  and  suggestive  theory  seems,  however, not  to  be  supported 
by  other  known  facts.     The  effects  of  different  chemicals  on  the  ciliary 

action  are  known,  and  it  is  not 
true  that  acids  produce  con- 
tinued reversal  of  the  cilia,  alka- 
lies the  opposite  effect,  as  would 
be  necessary  in  order  to  make 
this  explanation  satisfactory. 
Any  effective  chemical,  either 
acid  or  alkali,  produces,  as  we 
know,  the  avoiding  reaction, 
with  its  succession  of  coordinated 
Fig.  108.—  Diagram  of  the  effects  of  the  elec-  changes  in  the  ciliary  movements. 

trie  current  on  the  cilia    showing  that  the  regions       •  ag      Ludloff     (l8g5)    and 

where  the  ciha  are  directed  iorward  and  backward,        °         '  \       yo/ 

respectively,  do  not  correspond  to  the  regions  where  StatkewitSch  (1903)  SIIOW,  the 
the  current  is  leaving  and  entering  the  body.  characteristic     anodic     and    Cath- 

odic  effects  do  not  correspond  throughout  to  the  regions  where  the  cur- 
rent is  entering  or  leaving  the  protoplasm.  If  a  Paramecium  has  an 
oblique  position,  as  in  Fig.  108,  the  current  enters  the  body  on  the  entire 
left  side,  and  leaves  the  body  on  the  entire  right  side.  Hence,  on  the 
theory  we  are  considering,  all  the  cilia  of  the  left  side  ought  to  act 
alike,  and  in  the  opposite  manner  from  the  cilia  of  the  right  side. 
But  this  is  not  true.  On  the  left  side  the  cilia  of  the  region  b  beat  for- 
ward, those  of  c  backward ;  on  the  right  side  the  cilia  a  strike  forward, 
d  backward.  A  similar  distribution  of  the  discharge  of  trichocysts  under 
the  influence  of  the  induction  shock  is  shown  to  exist  by  Statkewitsch. 
The  distribution  of  the  effects  of  the  current  on  the  cilia  and  on  the 
trichocysts  therefore  does  not  correspond  to  the  distribution  of  the  regions 
where  the  current  is  entering  and  leaving  the  protoplasm;  hence  the 
latter  cannot  explain  the  former. 

Another  theory,  somewhat  less  definite  than  the  one  last  mentioned, 
but  widely  accepted,  is  the  following.     The  electric  current  is  conceived 


REACTIONS   OF  INFUSORIA    TO   ELECTRIC  CURRENT  167 

to  have  a  polarizing  effect  on  the  organism,  resulting  in  the  different 
action  of  the  cilia  on  the  two  halves.  At  the  anodic  half  the  current 
is  considered  to  cause  a  backward  movement  of  the  cilia,  or  "contractile 
stroke";  at  the  cathodic  half,  a  forward  movement  or  "expansive 
stroke"  (Verworn,  1899;  Ludloff,  1895).  The  precise  cause  of  this 
action  is  not  given,  but  as  supporting  the  possibility  of  this  view,  the 
experiments  of  Kuhne  (1864,  page  99)  and  Roux  (1891)  on  the  polariz- 
ing effects  of  the  current  may  be  cited.  Kuhne  showed  that  the  violet- 
colored  cells  of  Tradescantia  become  under  the  influence  of  the  electric 
current  red  at  the  anodic  end,  green  at  the  cathodic  end,  ■ —  indicating 
that  the  anodic  end  becomes  acid,  the  cathodic  end  alkaline.  Roux 
showed  that  under  the  electric  current  the  frog's  egg  becomes  divided 
into  two  halves  of  different  color.  Furthermore,  the  two  halves  of  a 
cell  in  the  electric  current  become  physically  somewhat  different,  owing  to 
the  cataphoric  action.  There  is  a  tendency  for  the  fluids  of  the  body 
to  be  carried  to  one  end,  —  the  cathodic,  —  while  the  solids  are  carried 
to  the  other,  —  the  anodic.  As  a  result  of  such  chemical  or  physical 
polarization,  or  of  both,  it  is  then  conceivable  that  the  body  of  the  in- 
fusorian  may  become  divided  into  two  halves,  differing  in  such  a  way 
that  the  cilia  act  in  opposite  directions.  On  this  view  the  backward 
stroke  of  the  cilia  on  the  anodic  half  of  the  body  is  as  much  a  specific 
effect  of  the  current  as  is  the  forward  stroke  of  the  cathodic  cilia.  Op- 
posed to  this  view  is  the  consideration  that  the  action  of  the  anodic  cilia 
is  as  a  matter  of  fact  not  different  from  that  in  the  unaffected  animal, 
and  the  further  fact  that  the  cathodic  effect  is  limited,  in  a  weak  cur- 
rent, to  only  the  cathodic  tip  of  the  animal.  If  both  the  backward  and 
the  forward  positions  of  the  cilia  are  specific  effects  of  the  current,  it 
is  difficult  to  see  why  the  former  should  prevail  so  strongly  over  the 
latter  in  a  weak  current.  On  the  other  hand,  if  we  consider  the  cathodic 
action  alone  as  a  specific  effect  of  the  current,  interfering  with  the  normal 
backward  stroke  of  the  cilia,  then  it  becomes  at  once  intelligible  that 
this  interference  should  be  least  in  a  weak  current,  and  should  increase 
as  the  current  becomes  more  powerful.  In  producing  its  characteristic 
effect  chiefly  at  the  cathode,  the  action  of  the  electric  current  on  in- 
fusoria agrees  with  its  action  on  muscle,  as  Bancroft  (1905)  has  recently 
pointed  out. 

The  most  thorough  study  of  the  fundamental  changes  produced  by 
the  electric  current  is  that  made  by  Statkewitsch  (1903  a),  and  his  con- 
clusions are  entitled  to  high  consideration.  Statkewitsch  subjected  Para- 
mecia  that  had  been  stained  in  the  living  condition  with  certain  chemical 
indicators,  —  neutral  red  and  phenol-phtalein,  —  to  the  influence  of  the 
electric  current.     He  found  that  the  current  caused  chemical  changes 


1 68  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

within  the  protoplasm,  the  endoplasmic  granules  and  vacuoles  becoming 
more  alkaline  in  reaction.  Statkewitsch  therefore  concludes  that  the 
peculiar  effect  of  the  electric  current  on  the  cilia  is  due  to  a  disturbance 
in  the  usual  equilibrium  of  the  chemical  processes  taking  place  in  the 
protoplasm.  The  results  of  this  disturbance  are  first  shown,  so  far  as 
the  ciliary  action  is  concerned,  in  the  cathodic  region,  spreading  thence 
over  the  remainder  of  the  body,  as  illustrated  in  Fig.  61. 

For  any  satisfactory  theory  of  the  reaction  to  the  electric  current, 
one  thing  is  essential;  it  must  account  for  the  cathodic  reversal  of  the 
cilia.  It  is  perfectly  clear  that  this  is  the  characteristic  feature  of  this 
reaction,  and  a  theory  that  will  account  for  this  reversal  will  at  once 
clear  up  the  curious  and  apparently  contradictory  effects  produced  under 
various  conditions.  Theories  which  do  not  take  this  into  account  are 
at  the  present  time  anachronisms ;  they  fail  to  touch  the  real  problem. 

Whatever  be  the  cause,  it  is  clear  that  the  behavior  of  infusoria  under 
the  action  of  the  electric  current  differs  radically  from  the  behavior  under 
other  conditions.  The  position  taken  by  the  organism  is  not  attained 
by  trial  of  varied  directions  of  movement,  as  in  the  reactions  to  most 
other  stimuli,  but  in  a  more  direct  way.  Different  parts  of  the  body 
are  differently  affected  by  the  current,  so  that  the  behavior  is  not  co- 
ordinated and  directed  toward  a  unified  end,  as  in  the  reactions  to  other 
stimuli.  The  motor  organs  of  the  different  parts  of  the  body  tend  to 
drive  the  animal  in  different  directions.  The  movement  actually  oc- 
curring is  a  resultant  of  these  differently  directed  factors.  It  is  there- 
fore sometimes  in  one  direction,  sometimes  in  another,  depending  on 
the  relative  strength  of  the  opposing  factors.  The  animal  thus  does 
not  approach  an  optimum  nor  cease  to  be  stimulated,  whatever  the 
direction  taken.  Sometimes  indeed  no  position  of  even  comparatively 
stable  equilibrium  is  possible  (Spirostomum). 

These  peculiarities  of  the  reaction  to  the  electric  current  are  due  to 
the  forced  reversal  of  the  cilia  in  the  cathodic  region  of  the  body,  —  an 
effect  not  produced  by  any  other  agent.  If  the  current  produced  only 
its  anodic  effect,  the  reaction  to  electricity  would  be,  so  far  as  the  evi- 
dence indicates,  precisely  like  that  to  other  agents.  The  cathodic  re- 
versal of  the  cilia  interferes  with  the  normal  behavior  of  the  organism. 
Thus  the  action  of  the  infusoria  under  the  electric  current  is  not  typical 
of  the  behavior  under  other  stimuli.  It  may  be  compared  to  the  be- 
havior of  an  organism  that  is  mechanically  held  by  clamps  and  thus 
prevented  from  showing  its  natural  behavior.  It  is  interesting  to  note 
that  this  cramped  and  incoherent  behavior  is  found  only  under  the  in- 
fluence of  an  agent  that  never  acts  on  the  animals  in  their  natural  exist- 
ence.    The  reaction  to  electricity  is  purely  a  laboratory  product. 


REACTIONS   OF  INFUSORIA    TO  ELECTRIC  CURRENT  169 

LITERATURE  IX 
Reactions  of  Infusoria  to  Electricity 

A.  Reactions  to  induction  shocks  :  Roesle,  1902  ;  Statkewitsch,  1903  ;  Biru- 
koff,  1899. 

B.  Reactions  to  the  constant  current:  Statkewitsch,  1903  a,  1904;  Wallen- 
gren,  1902,  1903;  Pearl,  1900;  Verworn,  1889  a,  1889  b,  1896;  Loeb  and  Bud- 
gett,  1897;  Dale,  1901 ;  Carlgren,  1899,  1905;  Bancroft,  1905;  Coehn  and 
Barratt,  1905. 


CHAPTER   X 

MODIFIABILITY     OF     BEHAVIOR     IN    INFUSORIA,   AND    BEHAVIOR 
UNDER   NATURAL   CONDITIONS.     FOOD    HABITS 

I.      MODIFIABILITY    OF    BEHAVIOR 

We  have  seen  that  in  Paramecium  the  behavior  varies  to  a  certain  ex- 
tent in  different  individuals  or  under  different  conditions.  Similar  varia- 
tions might  be  described  for  other  free  swimming  infusoria.  But  these 
observations  do  not  tell  us  whether  the  behavior  may  change  in  the  same 
individual  or  not.  Does  a  given  individual  always  react  in  the  same 
way  to  the  same  stimulus  under  the  same  conditions?  Or  may  the 
individual  itself  change,  so  that  it  behaves  differently  even  when  the 
external  conditions  remain  the  same,  —  as  we  know  to  be  the  case  in 
higher  animals?  To  answer  these  questions  it  is  necessary  to  follow 
continuously  the  behavior  of  a  single  individual,  and  this  can  be  done 
most  satisfactorily  in  attached  organisms,  such  as  Stentor  and  Vorticella. 
We  shall  base  our  account  on  the  usual  behavior  of  Stentor  rceselii,  which 
illustrates  well  the  points  in  which  we  are  at  present  interested. 

Stentor  rceselii  Ehr.  (Fig.  109)  is  a  colorless  or  whitish,  trumpet- 
shaped  animal,  consisting  of  a  slender,  stalklike  body,  bearing  at  its 
end  a  broadly  expanded  disk,  the  peristome.  The  surface  of  the  body 
is  covered  with  longitudinal  rows  of  fine  cilia,  while  the  edge  of  the  disk 
is  surrounded  by  a  circlet  of  large  compound  peristomal  cilia  or  mem- 
branellas.  These  make  a  spiral  turn,  passing  on  the  left  side  into  the 
large  buccal  pouch,  which  leads  to  the  mouth.  The  mouth  thus  lies 
on  the  edge  of  the  disk,  nearly  in  the  middle  of  what  may  be  called  the 
oral  or  ventral  surface  of  the  body.  The  smaller  end  of  the  body  is 
known  as  the  foot;  here  the  internal  protoplasm  is  exposed,  sending 
out  fine  pseudopodia,  by  which  the  animal  attaches  itself. 

Stentor  rceselii  is  usually  attached  to  a  water  plant  or  a  bit  of  debris 
by  the  foot,  and  the  lower  half  of  the  body  is  surrounded  by  the  so-called 
tube.  This  is  a  verv  irregular  sheath  formed  by  a  mucus-like  secretion 
from  the  surface  of  the  body,  in  which  are  embedded  flocculent  materials 
of  all  sorts.  It  is  frequently  nearly  transparent,  so  as  to  be  almost  in- 
visible. Stentor  rceselii  is  found  in  marshy  pools,  where  much  dead 
vegetation  is  present,  but  where  decay  is  taking  place  only  slowly. 

170 


MODIFI ABILITY   OF  BEHAVIOR 


171 


In  the  extended  animal  the  peristomal  cilia  are  in  continual  motion. 
When  finely  ground  India  ink  or  carmine  is  added  to  the  water,  the 
currents  caused  by  the  cilia  are  seen  to  be  as  follows:  The  mouth  of 
the  animal  forms  the  bottom  of  a  vortex,  toward  which  the  water  above 
the  disk  descends  from  all  sides  (Fig.  109).     Only  the  particles  near 


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Fig.  109.  —  Stentor  r&selii,  showing  the  currents  caused  by  the  cilia  of  the  peristome. 

the  axis  of  the  vortex  really  strike  the  disk;  those  a  little  to  one  side 
shoot  by  the  edges  without  touching.  Particles  which  reach  the  disk 
pass  to  the  left,  toward  the  buccal  pouch,  following  thus  a  spiral  course. 
Reaching  the  buccal  pouch,  they  are  whirled  about  within  it  a  few 
times ;  then  they  either  pass  into  the  mouth,  at  the  bottom  of  the  pouch, 
or  they  are  whirled  out  over  the  edge  of  the  pouch,  at  the  mid-ventral 
notch.  In  the-  latter  case  they  usually  pass  backward  along  the  mid- 
ventral  line  of  the  body  (Fig.  109,  a),  till  they  reach  the  edge  of  the  tube. 
To  this  they  may  cling,  thus  aiding  to  build  up  the  tube. 

When  stimulated,  Stentor  roeselii  may  contract  into  its  tube,  taking 
then  a  short  oblong  or  conical  form  (Fig.  no).     Such  contractions  do 


172  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

not  as  a  rule  take  place  save  in  response  to  well-marked  stimuli.     When 

not  disturbed  in  any  way,  the  animal  remains  extended,  with  cilia  in 

active  operation. 

Let  us  try  the  effect  of  disturbing  the  animal  very  slightly.     While 

the  disk  is  widely  spread  and  the  cilia  are  actively  at  work,  we  cause  a 
fine  current  of  water  to  act  upon  the  disk,  in  the 
following  way.  A  long  tube  is  drawn  to  a  very  fine 
capillary  point  and  filled  with  water.  The  capillary 
tip  is  brought  near  the  Stentor,  while  the  long  tube 
is  held  nearly  perpendicular.  The  pressure  causes 
a  jet  of  water  from  the  tip  to  strike  the  disk  of  the 
animal.  Like  a  flash  it  contracts  into  its  tube.  In 
about  half  a  minute  it  extends  again,  and  the  cilia 

*IG.  no.  —  Stentor  .    .  i 

rceseia  contracted  into  resume  their  activity.  Now  we  cause  the  current  to 
lts  tube-  act  again  upon  the  disk.     This  time  the  animal  does 

not  contract,  but  continues  its  normal  activities  without  regard  to 
the  current  of  water.  This  experiment  may  be  repeated  on  other  indi- 
viduals; invariably  they  react  to  the  current  the  first  time,  then  no 
longer  react.  The  same  results  are  obtained  with  other  fixed  infuso- 
ria: Epistylis  and  Carchesium.  By  using  other  very  faint  stimuli, 
such  as  that  produced  by  touching  the  surface  film  of  the  water  close 
to  the  organism,  or  by  slightly  jarring  the  object  to  which  it  is  at- 
tached, the  same  results  are  obtained.  To  the  first  stimulus  they 
respond  sharply ;  to  the  second  and  following  ones  they  do  not  respond 
at  all,  even  if  long  continued. 

Thus  the  organism  becomes  changed  in  some  way  after  its  first 
reaction,  for  to  the  same  stimulus,  under  the  same  external  conditions, 
it  no  longer  reacts.  What  is  the  nature  of  this  internal  change?  The 
first  suggestion  that  rises  to  the  mind  in  explanation  of  such  a  cessation 
of  reaction  is  that  it  may  be  due  to  fatigue.  The  distinction  between 
fatigue  and  other  changes  of  condition  is  an  important  one,  for  the 
following  reason.  Fatigue  is  due  to  what  may  be  called  a  failure.  It 
is  an  imperfection  inherent  perhaps  in  the  nature  of  the  material  of 
which  organisms  are  composed,  preventing  them  from  doing  what  might 
be  to  their  advantage.  Changes  of  reaction  due  to  other  causes  might 
on  the  other  hand  be  regulatory,  tending  to  the  advantage  of  the  or- 
ganism. Higher  animals  often  react  strongly  by  a  "start,"  to  the  first 
incidence  of  sudden  harmless  stimuli,  then  no  longer  react,  and  this 
cessation  is  evidently  a  regulation  of  behavior  that  is  to  the  interest  of 
the  organism.  We  must  then  determine  whether  the  failure  of  the  in- 
fusorian  to  react  to  the  second  stimulation  is  due  to  fatigue  or  to  some 
other   cause. 


M0DIF1 ABILITY   OF  BEHAVIOR  173 

It  seems  improbable  that  the  change  of  behavior  is  due  to  fatigue, 
since  the  change  occurs  after  but  a  single  stimulation  and  a  single  reac- 
tion. It  could  hardly  be  supposed  that  these  would  fatigue  the  animal 
to  such  an  extent  as  to  prevent  further  contractions.  And  if  we  use 
stronger  stimuli,  we  find  that  the  animal  continues  to  contract  succes- 
sively every  time  the  stimulus  is  applied,  for  an  hour  or  more.  It  is 
evident  that  the  failure  to  contract  after  the  first  stimulation  cannot  be 
due  to  fatigue  of  the  contractile  apparatus. 

If  we  make  the  stimulation  somewhat  stronger  than  in  our  first  ex- 
periments, as  may  be  done  by  touching  the  animal  lightly  with  a  capil- 
lary glass  rod,  the  behavior  is  a  little  different.  The  animal  may  react 
the  first  and  second  times,  then  cease  to  react,  or  it  may  react  half  a 
dozen  times,  or  more,  then  cease.  If  we  continue  the  stimuli,  we  find  a 
change  in  the  behavior.  The  animal  instead  of  contracting  bends  into 
a  new  position,  and  it  may  do  this  repeatedly.  This  shows  that  the  fail- 
ure to  contract  is  not  due  to  a  failure  to  perceive  the  stimulus,  —  in 
other  words,  to  a  fatigue  of  the  perceptive  power,  —  for  the  bending 
into  a  new  position  shows  that  the  stimulus  is  perceived,  though  the 
reaction  differs  from  the  first  one. 

Our  results  thus  far  show  that  after  responding  once  or  a  few  times 
to  very  weak  stimulation,  the  organism  becomes  changed,  so  that  it 
no  longer  reacts  as  before,  and  that  this  change  is  not  due  to  fatigue, 
either  of  the  contractile  apparatus  or  of  the  perceptive  power.  The 
behavior  may  then  be  of  the  same  regulatory  character  as  is  the  similar 
behavior  in  higher  animals.  Indeed,  so  far  as  the  objective  evidence 
goes,  this  behavior  in  Stentor  precisely  resembles  that  of  higher  ani- 
mals, and  is  to  the  same  degree  in  the  interest  of  the  organism. 

With  still  stronger  stimulation,  produced  by  touching  the  animal 
with  the  capillary  glass  rod,  another  curious  phenomenon  often  shows 
itself.  The  animal  may  react  to  each  of  the  first  half  dozen  strokes, 
then  cease  to  react;  then  after  a  few  more  strokes  react  again,  then 
cease  to  react  till  a  large  number  have  been  given,  and  so  continue. 
A  typical  series,  giving  the  number  of  strokes  before  contraction  is 
produced,  is  the  following,  obtained  from  experiments  with  an  individ-^ 
ual  of  Epistylis:  — 

1  —  22  —  10  —  3  —  3  —  1  —  1  —  22  —  59  —  125  (continuous  blows 
for  one  minute) — (f  minutes) — (i|  minutes)  —  (4^  minutes). 

During  such  experiments  the  organism,  when  it  does  not  contract, 
continually  changes  its  position,  as  if  trying  to  escape  the  blows.  The 
reason  for  the  contraction  at  irregular  intervals  which  become  longer 
as  the  experiment  continues,  is  not  clear.  Possibly  fatigue  may  have 
something  to  do  with  this  matter. 


174 


BEHAVIOR   OF    THE   LOWER   ORGANISMS 


m 


The  stimuli  with  which  we  have  thus  far  dealt  are  not  directly  in- 
jurious, and  do  not  interfere  in  the  long  run  with  the  normal  functions 
of  the  organism,  so  that  the  power  of  becoming  accustomed  to  them 
and  ceasing  to  react  is  useful.  Let  us  now  examine  the  behavior  under 
conditions  which  are  harmless  when  acting  for  a  short  time,  but  which, 
when  continued,  do  interfere  with  the  normal  functions.  Such  condi- 
tions rriay  be  produced  by  bringing  a  large  quantity  of  fine  particles, 
such  as  India  ink  or  carmine,  by  means  of  a  capillary  pipette,  into  the 
water  currents  which  are  carried  to  the  disk  of  Stentor  (Fig.  in). 

Under  these  circumstances  the  normal  movements  are  at  first  not 
changed.     The  particles  of  carmine  are  taken  into  the  pouch  and  into 

the  mouth,  whence  they  pass  into  the  internal 
protoplasm.  If  the  cloud  of  particles  is  very 
dense,  or  if  it  is  accompanied  by  a  slight  chem- 
ical stimulus,  as  is  usually  the  case  with  the 
carmine  grains,  this  behavior  lasts  but  a  short 
time;  then  a  definite  reaction  supervenes. 
The  animal  bends  to  one  side  —  always,  in 
the  case  of  Stentor,  toward  the  aboral  side. 
It  thus  as  a  rule  avoids  the  cloud  of  particles, 
unless  the  latter  is  very  large.  This  simple 
method  of  reaction  turns  out  to  be  more 
effective  in  getting  rid  of  stimuli  of  all  sorts 
than  might  be  expected.  If  the  first  reaction 
is  not  successful,  it  is  usually  repeated  one  or 
more  times.  This  reaction  corresponds  closely 
with  the  "avoiding  reaction"  of  free-swim- 
ming infusoria,  and  like  the  latter,  is  usually 
accompanied  by  revolution  on  the  long  axis, 
—  the  animal  twisting  on  its  stalk  two  or  three 
times  as  it  bends  toward  the  aboral  side. 
Fig.  in.— A  cloud  of  car-         If   the   repeated  turning  toward  one  side 

mine  is  introduced  into  the  water     ,  ,.  ■,  .         ,  .  . 

currents  passing  to  the  mouth  does  not  relieve  the  animal,  so  that  the  parti - 
of  stentor.  c[es  0f  carmine  continue  to  come  in  a  dense 

cloud,  another  reaction  is  tried.  The  ciliary  movement  is ,  suddenly 
reversed  in  direction,  so  that  the  particles  against  the  disk  and  in  the 
pouch  are  thrown  off.  The  water  current  is  driven  away  from  the 
disk  instead  of  toward  it.  This  lasts  but  an  instant,  then  the  current 
is  continued  in  the  usual  way.  If  the  particles  continue  to  come,  the 
reversal  is  repeated  two  or  three  times  in  rapid  succession.  If  this 
fails  to  relieve  the  organism,  the  next  reaction  —  contraction  —  usually 
supervenes. 


M0DIF1 ABILITY   OF  BEHAVIOR  175 

Sometimes  the  reversal  of  the  current  takes  place  before  the  turn- 
ing away  described  first ;  it  may  then  be  followed  by  the  turning  away. 
But  usually  the  two  reactions  are  tried  in  the  order  we  have  given. 

If  the  Stentor  does  not  get  rid  of  the  stimulation  in  either  of  the 
ways  just  described,  it  contracts  into  its  tube.  In  this  way  it  of  course 
escapes  the  stimulation  completely,  but  at  the  expense  of  suspending 
its  activity  and  losing  all  opportunity  to  obtain  food.  The  animal 
usually  remains  in  the  tube  about  half  a  minute,  then  extends.  When 
its  body  has  reached  about  two-thirds  its  original  length,  the  ciliary 
disk  begins  to  unfold  and  the  cilia  to  act,  causing  currents  of  water  to 
reach  the  disk,  as  before. 

We  have  now  reached  a  specially  interesting  point  in  the  experi- 
ment. Suppose  that  the  water  currents  again  bring  the  carmine  grains. 
The  stimulus  and  all  the  external  conditions  are  the  same  as  they  were 
at  the  beginning?  Will  the  Stentor  behave  as  it  did  at  the  beginning? 
Will  it  at  first  not  react,  then  bend  to  one  side,  then  reverse  the  current, 
then  contract,  passing  anew  through  the  whole  series  of  reactions? 
Or  shall  we  find  that  it  has  become  changed  by  the  experiences  it  has 
passed  through,  so  that  it  will  now  contract  again  into  its  tube  as  soon 
as  stimulated? 

We  find  the  latter  to  be  the  case.  As  soon  as  the  carmine  again 
reaches  its  disk,  it  at  once  contracts  again.  This  may  be  repeated 
many  times,  as  often  as  the  particles  come  to  the  disk,  for  ten  or  fifteen 
minutes.  Now  the  animal  after  each  contraction  stays  a  little  longer 
in  the  tube  than  it  did  at  first.  Finallv  it  ceases  to  extend,  but  contracts 
repeatedly  and  violently  while  still  enclosed  in  its  tube.  In  this  way 
the  attachment  of  its  foot  to  the  object  on  which  it  is  situated  is  broken, 
and  the  animal  is  free.  Now  it  leaves  its  tube  and  swims  away.  In 
leaving  the  tube  it  may  swim  forward  out  of  the  anterior  end  of  the  tube ; 
but  if  this  brings  it  into  the  region  of  the  cloud  of  carmine,  it  often  forces 
its  way  backward  through  the  substance  of  the  tube,  and  thus  gains  the 
outside.     Here  it  swims  away,  to  form  a  new  tube  elsewhere. 

While  swimming  freely  after  leaving  its  tube,  Stentor  shows  the 
characteristic  behavior  of  the  free-swimming  infusoria,  such  as  Para- 
mecium. Upon  this,  therefore,  we  need  not  dwell,  passing  at  once  to 
the  behavior  in  becoming  reattached  and  forming  a  new  tube. 

On  coming  to  the  surface  film  of  the  water,  or  the  surface  of  solid 
objects,  the  free-swimming  Stentor  behaves  in  a  peculiar  way.  It 
applies  its  partially  unfolded  disk  to  the  surface  and  creeps  rapidly 
over  it,  the  ventral  side  of  the  body  being  bent  over  close  to  the 
surface.  It  may  thus  creep  over  a  heap  of  debris,  following  all  the 
irregularities  of  the  surface  rapidly  and  neatly,  seeming  to  explore  it 


176 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


thoroughly.  This  may  last  for  some  time,  then  the  animal  may  leave 
the  debris  and  swim  about  again.  Other  heaps  of  debris  or  the  sur- 
faces of  solids  are  explored  in  the  same  way.  Finally,  after  ten  or  twenty 
minutes  or  more,  one  of  these  is  selected  for  the  formation  of  a  new  tube. 
It  may  be  seen  that  as  the  Stentor  moves  about  a  viscid  mucus  is  se- 
creted over  the  surface  of  the  body.  To  this  mucus  particles  of  debris 
stick  and  are  trailed  behind  the  swimming  animal.  In  a  certain  region, 
perhaps  between  two  masses  of  debris,  the  animal  stops  and  begins  to 
move  backward  and  forward  with  an  oscillatory  motion,  through  a  dis- 
tance about  two-thirds  its  contracted  length.  This  movement,  in  pre- 
cisely the  same  place,  is  kept  up  for  about  two  minutes,  while  the  mucus 

from  the  surface  is  rapidly  secreted. 
The  movement  compacts  this  mucus 
into  a  short  tube  or  sheath,  —  the  tube 
in  which  the  Stentor  is  to  live.  The 
process  is  represented  in  Fig.  112. 
Next  the  tip  of  the  foot  is  pressed 
against  the  debris  at  the  bottom  of  the 
tube.  There  it  adheres  by  means  of 
Fig.  112. —  Oscillating  movement  of  nne  pseudopodia  sent  out  from  the  in- 

Stentor,  by  which  it  forms  a  new  tube.  ,  .  ,T  ,        „ 

i-2,  alternating  positions,  o,  the  secreted  ternal  protoplasm.  Now  the  Stentor 
mucus;  b,  masses  of  debris.  extends  to  full  length,   and  we  find  it 

in  the  usual  attached  condition,  with  the  lower  half  of  the  body 
surrounded  by  a  transparent  tube  of  mucus.  The  Stentor  has  thus 
moved  away  from  the  place  where  it  was  subjected  to  the  mass  of  car- 
mine particles,  and  has  established  itself  in  another  situation. 

The  behavior  just  described  shows  clearly  that  the  same  individual 
does  not  react  always  in  the  same  way  to  the  same  stimulus.  The 
stimulus  and  the  other  external  conditions  remaining  the  same,  the 
organism  responds  by  a  series  of  reactions  becoming  of  more  and 
more  pronounced  character,  until  by  one  of  them  it  rids  itself  of  the 
stimulation.  Under  the  conditions  described  —  when  a  dense  cloud 
of  carmine  is  added  to  the  water  —  the  changes  in  the  behavior  may  be 
summed  up  as  follows :  — 

(1)  No  reaction  at  first:  the  organism  continues  its  normal  activi- 
ties for  a  short  time. 

(2)  Then  a  slight  reaction  by  turning  into  a  new  position,  —  a  seem- 
ing attempt  to  keep  up  the  normal  activities  and  yet  get  rid  of  the 
stimulation. 

(3)  If  this  is  unsuccessful,  we  have  next  a  slight  interruption  of  the 
normal  activities,  in  a  momentary  reversal  of  the  ciliary  current,  tending 
to  get  rid  of  the  source  of  stimulation. 


MODIFI ABILITY   OF  BEHAVIOR  177 

(4)  If  the  stimulus  still  persists,  the  animal  breaks  off  its  normal 
activity  completely  by  contracting  strongly  —  devoting  itself  entirely, 
as  it  were,  to  getting  rid  of  the  stimulation,  though  retaining  the  possi- 
bility of  resuming  its  normal  activity  in  the  same  place  at  any  moment. 

(5)  Finally,  if  all  these  reactions  remain  ineffective,  the  animal  not 
only  gives  up  completely  its  usual  activities,  but  puts  in  operation 
another  set,  having  a  much  more  radical  effect  in  separating  the  animal 
from  the  stimulating  agent.  It  abandons  its  tube,  swims  away,  and 
forms  another  one  in  a  situation  where  the  stimulus  does  not  act  upon  it. 

The  behavior  of  Stentor  under  the  conditions  given  is  evidently  a 
special  form  of  the  method  of  the  selection  of  certain  conditions  through 
varied  activities,  —  a  form  which  we  have  not  met  before.  The  organ- 
ism "tries"  one  method  of  action;  if  this  fails,  it  tries  another,  till  one 
succeeds.  Like  other  behavior  based  on  this  method,  it  is  not  a  specific 
reaction  to  any  one  stimulus,  but  is  seen  whenever  analogous  conditions 
are  produced  in  any  way.  Thus  we  may  use  in  place  of  carmine  other 
substances.  Chemicals  of  different  kinds  produce  a  similar  series  of 
reactions.  A  decided  change  in  osmotic  pressure  has  a  somewhat 
similar  effect.  There  are  variations  in  the  details  of  the  reaction  series 
under  different  conditions.  Sometimes  one  step  or  another  is  omitted, 
or  the  order  of  the  different  steps  is  varied.  But  it  remains  true  that 
under  conditions  which  gradually  interfere  with  the  normal  activities 
of  the  organism,  the  behavior  consists  in  "trying"  successively  different 
reactions,  till  one  is  found  that  affords  relief.  The  production  of  any 
given  step  in  the  behavior  cannot  be  explained  as  a  necessary  conse- 
quence of  the  preceding  step.  On  the  contrary,  the  bringing  into  opera- 
tion of  any  given  step  depends  upon  the  ineffectiveness  of  the  preceding 
ones  in  getting  rid  of  the  stimulating  condition.  The  series  may  cease 
at  any  point,  as  soon  as  the  stimulus  disappears.  Moreover,  it  is  evi- 
dent that  the  succeeding  steps  are  not  mere  accentuations  of  the  pre- 
ceding ones,  but  differ  completely  in  character  from  them,  being  based 
upon  different  methods  of  getting  rid  of  the  stimulation. 

All  our  results  on  Stentor  then  show  clearly  that  the  same  organism 
may  react  to  the  same  stimulus  in  various  different  ways.  It  may  react 
at  first,  then  cease  to  react  if  the  stimulus  does  not  interfere  with  its 
normal  activities;  it  may  react  at  first  by  a  very  pronounced  reaction 
(contraction),  then  later  by  a  very  slight  reaction  (bending  over  to  one 
side) ;  or  it  may  respond,  if  the  stimulus  does  interfere  with  its  normal 
functions,  by  a  whole  series  of  different  reactions,  becoming  of  a  more 
and  more  pronounced  character.  Since  in  each  of  these  cases  the  ex- 
ternal conditions  remain  throughout  the  same,  the  change  in  reaction 
must  be  due  to  a  change  in  the  organism.     The  organism  which  reacts 

N 


178  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

to  the  carmine  grains  by  contracting  or  by  leaving  its  tube  must  be  differ- 
ent in  some  way  from  the  organism  which  reacted  to  the  same  stimulus 
by  bending  to  one  side.  No  structural  change  is  evident,  so  that  all 
we  can  say  is  that  the  physiological  state  0}  the  organism  lias  changed.  The 
same  organism  in  different  physiological  states  reacts  differently  to  the 
same  stimuli.  It  is  evident  that  the  anatomical  structure  of  the  organ- 
ism and  the  different  physical  or  chemical  action  of  the  stimulating 
agents  are  not  sufficient  to  account  for  the  reactions.  The  varying  physio- 
logical states  of  the  animal  are  equally  important  factors.  In  Stentor 
we  are  compelled  to  assume  at  least  five  different  physiological  states  to 
account  for  the  five  different  reactions  given  under  the  same  conditions. 
We  shall  later  find  much  occasion  to  realize  the  importance  of  physiologi- 
cal states  in  determining  behavior. 

These  relations  may  be  stated  from  another  point  of  view,  which 
leads  to  interesting  questions.  The  present  physiological  state  of  an 
organism  depends  upon  its  past  history,  so  that  we  can  say  directly 
that  the  behavior  of  such  an  organism  as  Stentor  under  given  conditions 
depends  on  its  past  history.  This  statement  we  know  is  markedly 
true  for  higher  organisms.  What  a  higher  animal  does  under  certain 
conditions  depends  upon  its  experience :  —  that  is,  upon  its  past  history. 
In  the  typical  and  most  interesting  case  we  say  that  the  behavior  of  the 
higher  organism  depends  upon  what  it  has  learned  by  experience.  Is 
the  change  in  the  behavior  of  Stentor  in  accordance  with  its  past  history 
a  phenomenon  in  any  wise  similar  in  character  to  the  learning  of  a  higher 
organism?  In  judging  of  this  question  we  must  rely,  of  course,  entirely 
upon  objective  evidence ;  —  upon  what  can  be  actually  observed. 
When  this  is  done,  it  is  hard  to  discover  any  ground  for  making  a  dis- 
tinction in  principle  between  the  two  cases.  The  essential  point  seems 
to  be  that  after  experience  the  organism  reacts  in  a  more  effective  way 
than  before.  The  change  in  reaction  is  regulatory,  not  merely  hap- 
hazard. And  this  is  as  clearly  the  case  in  Stentor  as  in  the  higher 
organism.  It  is  true  that,  so  far  as  we  can  see,  the  behavior  of  Stentor 
shows  in  only  a  rudimentary  way  phenomena  that  become  exceedingly 
striking  and  complex  in  higher  organisms.  Stentor  seems  to  vary  its 
behavior  only  in  accordance  with  the  experience  that  either  (1)  the 
stimulus  to  which  a  strong  reaction  is  at  first  given,  does  not  really 
interfere  with  its  activities,  so  that  reaction  ceases;  or  (2)  that  the  reac- 
tion already  given  is  ineffective,  since  the  interference  with  its  activities 
continues,  so  that  another  reaction  is  introduced.1     If  the  changes  in 

1  It  is  to  be  noted  that  nothing  is  said  in  this  statement  as  to  the  Stentor's  perceiving 
these  relations.  The  statement  attempts  merely  a  formulation  of  the  observed  facts  in 
such  a  way  as  to  bring  out  their  relation  to  what  we  observe  in  higher  organisms. 


BEHAVIOR    UNDER  NATURAL   CONDITIONS  179 

the  behavior  of  Stentor  were  not  regulatory,  becoming  more  fitted  to  the 
existing  conditions,  a  comparison  with  the  behavior  of  higher  animals 
in  learning  would  be  out  of  place.  But  since  the  changes  clearly  are 
regulatory,  in  the  one  case  as  in  the  other,  it  would  be  equally  out  of 
place  to  deny  their  similarity,  in  this  respect  at  least. 

In  another  important  feature  the  behavior  of  Stentor  falls,  so  far  as 
our  present  evidence  goes,  far  below  the  level  of  that  found  in  the  learn- 
ing of  higher  animals.  The  modification  in  the  behavior  induced  by 
experience  seems  to  last  but  a  very  short  time.  Immediately  after 
reacting  in  one  way,  which  proves  ineffective,  it  reacts  in  another.  But 
a  short  time  after  it  apparently  reacts  in  the  same  way  as  at  first.1  As 
a  rule,  it  is  evidently  to  the  interest  of  an  organism  living  under  such  sim- 
ple conditions  as  Stentor  to  return  to  the  first  method  of  reaction  when 
again  stimulated  after  a  period  of  quiet,  for  as  a  rule  this  first  method 
is  effective,  and  it  would  be  most  unfortunate  for  the  Stentor  to  proceed 
to  the  extremity  of  abandoning  its  tube  without  a  trial  of  simpler 
reactions.  But  the  difference  between  behavior  which  is  modified 
only  for  a  few  moments  after  an  experience,  and  that  which  is  per- 
manently modified,  is  undoubtedly  important.  The  latter  would  never- 
theless be  developed  from  the  former  by  a  mere  quantitative  change, 
so  that  the  variation  in  duration  does  not  constitute  a  difference  in  essen- 
tial nature. 

We  may  sum  up  the  results  of  the  present  section  as  follows :  The 
same  individual  does  not  always  behave  in  the  same  way  under  the  same 
external  conditions,  but  the  behavior  depends  upon  the  physiological 
condition  of  the  animal.  The  reaction  to  any  given  stimulus  is  modified 
by  the  past  experience  of  the  animal,  and  the  modifications  are  regula- 
tory, not  haphazard,  in  character.  The  phenomena  are  thus  similar 
to  those  shown  in  the  "  learning  "  of  higher  organisms,  save  that  the  modi- 
fications depend  upon  less  complex  relations  and  last  a  shorter  time. 

2.    The  Behavior  of  Infusoria  under  Natural  Conditions 

We  have  thus  far  dealt  chiefly  with  the  behavior  of  infusoria  under 
experimental  conditions.     In  experiments   the   conditions   are  usually 

1  This  matter  cannot  be  considered  definitely  settled.  It  is  exceedingly  difficult 
in  practice  to  devise  and  carry  out  experiments  which  shall  actually  determine  the 
length  of  time  that  the  modified  behavior  lasts.  A  thorough,  definitely  planned  investi- 
gation should  be  directed  precisely  upon  this  point.  Hodge  and  Aikins  (1895)  report 
that  Vorticella,  which  at  first  took  yeast  as  food,  later  rejected  the  yeast,  and  that  for 
"several  hours"  it  refused  to  take  the  yeast  again.  But  unfortunately  no  further 
details  are  given.  We  do  not  know  whether  the  Vorticella  was  injured  and  took 
no  food  at  all,  or  what  other  conditions  were  present,  so  that  we  can  build  little  upon 
this  observation. 


180  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

made  as  simple  as  possible.  All  sources  of  stimulation  save  one  are 
excluded,  in  order  that  we  may  discover  the  precise  effects  of  that  one. 
In  our  account  of  Paramecium  we  have  seen  that  when  more  than  one 
source  of  stimulation  is  present,  the  behavior  is  determined  by  all  the 
existing  conditions,  so  that  often  the  behavior  cannot  be  characterized  as 
a  precise  reaction  to  a  definite  stimulus.  That  this  is  true  also  for  other 
infusoria  we  have  seen  in  a  number  of  instances,  particularly  in  our  ac- 
count of  the  contact  reaction.  It  would  be  possible  to  add  many  other 
examples  to  these,  making  a  special  chapter  on  "Reactions  to  Two  or 
More  Stimuli,"  but  this  would  add  no  new  principle  to  what  we  have 
already  brought  out.  The  general  statement  may  be  made,  that  to 
account  for  the  way  an  infusorian  behaves  at  a  given  time,  it  is  as  a  rule 
not  sufficient  to  take  into  account  a  single  source  of  stimulation,  but  all 
the  conditions  must  be  considered. 

We  shall  now  look  at  certain  features  of  the  behavior  of  infusoria 
under  the  conditions  that  are  supplied  by  the  environment,  in  all  their 
variety  and  complexity.  We  wish  to  see  how  the  natural  "wild"  or- 
ganism behaves.  Our  account  cannot  be  exhaustive,  for  the  natural 
history  of  the  thousands  of  species  of  infusoria  remains  largely  to  be 
worked  out.  We  shall  merely  examine  certain  typical  features  of  the 
behavior,  devoting  especial  attention  to  the  food  reactions. 

In  our  chapter  on  the  "Action  System"  we  have  seen  some  of  the 
chief  variations  in  the  natural  behavior  of  infusoria.  We  have  there  seen 
that  the  infusoria  can  be  divided,  according  to  their  methods  of  life,  into 
three  main  groups :  those  that  are  attached,  those  that  creep  over  sur- 
faces, and  those  that  swim  freely.  The  behavior  in  these  different  groups 
necessarily  differs  much.  Yet,  as  we  have  seen,  every  possible  gradation 
exists  from  one  group  to  another,  and  even  the  same  individual  may  at 
different  periods  represent  each  different  group.  The  behavior  is  sim- 
plest and  least  varied  in  the  free-swimming  organisms ;  more  varied  in 
those  which  habitually  creep  along  a  surface;  most  complex  in  those 
which  live  attached.  The  reason  for  this  seems  to  be  as  follows :  In 
the  open  water  the  conditions  are  exceedingly  simple.  The  free-swim- 
ming organism  may  escape  an  injurious  stimulus  simply  by  swimming 
away.  In  the  fixed  organism,  on  the  other  hand,  the  conditions  are  more 
complex.  At  any  moment  both  the  solid  and  the  free  fluid  are  acting 
on  the  organism.  For  a  fixed  animal  to  obtain  food  and  escape  injurious 
conditions,  varied  devices  are  necessary.  It  cannot  at  once  solve  any 
difficulty  by  departing,  as  the  free  organism  can.  We  find,  then,  that 
such  fixed  organisms  have  developed  varied  reaction  methods  (see  the 
preceding  chapter). 

There  is  much  variation  in  the  complexity  of  behavior  even  among 


BEHAVIOR   UNDER  NATURAL   CONDITIONS  181 

species  living  under  similar  conditions.  Some  of  the  free-swimming 
species  are  very  supple,  changing  form  continually.  Such  is  the  case, 
for  example,  with  Lacrymaria  olor,  which  stretches  its  long  neck  in 
every  direction,  shortens  it  until  it  has  almost  disappeared,  reextends  it, 
and  seems  to  explore  thoroughly  the  surrounding  region.  Such  an 
organism  has,  of  course,  much  better  opportunity  for  effective  behavior 
by  the  method  of  trial  than  has  such  a  rigid  form  as  Paramecium. 

Similar  differences  are  found  among  the  creeping  infusoria,  and 
among  the  fixed  species.  Some  fixed  infusoria  contract  frequently, 
while  others  contract  only  rarely.  In  some  cases  the  contraction  occurs 
at  regular  intervals,  even  when  there  is  no  indication  of  an  external 
stimulus.  This  is  the  case  with  Vorticella.  There  is  no  evidence  that 
in  infusoria  periods  of  rest,  comparable  with  the  sleep  of  higher  animals, 
are  alternated  with  periods  of  activity.  Hodge  and  Aikins  (1895) 
kept  a  single  Vorticella  continuously  under  observation  for  twenty-one 
hours,  besides  intermittent  study  for  a  number  of  clays.  They  found 
that  there  was  no  period  of  inactivity.  During  five  days  the  cilia  were 
in  continuous  motion,  food  was  continuously  taken,  and  contractions 
were  repeated  at  brief  intervals. 

A  number  of  fixed  infusoria  live,  like  Stentor  rceselii,  in  tubes,  some 
gelatinous,  some  membranous  in  character.  As  a  rule  these  tubes  are 
formed  in  a  very  simple  manner.  The  material  of  which  they  are  com- 
posed is  secreted  by  the  outer  surface  of  the  animal.  In  the  repeated 
contractions  and  extensions  of  the  body  this  material  is  worked  off,  in 
the  form  of  a  sheath.  The  tube  may  become  thicker  by  the  secretion 
of  more  material  on  the  surface  of  the  animal.  It  often  grows  in  length, 
either  as  the  animal  becomes  longer  or  as  it  migrates  farther  out  toward 
the  open  end  of  the  tube.  In  the  secreted  material,  which  is  often  trans- 
parent, all  sorts  of  foreign  substances  may  become  embedded,  in  the 
following  way:  They  are  carried  as  particles  to  the  oral  disk  by  the  cilia. 
Thence  they  pass  backward  over  the  surface  of  the  body,  till  they  reach 
the  gelatinous  substance  of  the  tube,  where  they  become  embedded. 
Thus  in  most  cases  the  formation  of  the  tube  seems  a  direct  consequence 
of  the  secretion  of  the  mucus-like  substance  over  the  body  of  the  animal, 
taken  in  connection  with  the  usual  movements.  The  intervention  of  any 
special  type  of  behavior  directed  toward  the  end  of  forming  the  tube 
seems  unnecessary.  But  in  some  cases,  as  we  have  seen  in  our  account 
of  Stentor,  the  tube  is  formed  at  the  beginning  by  a  definite  set  of  move- 
ments, of  a  character  especially  fitted  to  produce  such  a  structure.  For 
details  as  to  different  kinds  of  tubes,  and  their  structure  and  method 
of  formation,  reference  may  be  made  to  Butschli's  great  work  on  the 
infusoria  (1889). 


182  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

A  set  of  phenomena  that  is  deserving  of  careful  study  for  its  implica- 
tions as  to  the  nature  of  behavior  is  that  involved  in  the  activities  pre- 
liminary to  conjugation.  It  is  possible  that  the  organisms  are  in  a 
modified  physiological  condition  at  this  time,  behaving  differently  from 
usual.  Critical  observations  on  this  subject,  of  such  a  nature  that  we 
can  use  them  for  our  present  purpose,  are  too  few  in  number  to  make 
possible  a  unified  account  of  these  phenomena.  An  account  of  the 
facts  for  Paramecium  is  given  on  page  102.  The  field  is  one  deserving 
of  much  further  work. 

3.    Food  Habits 

The  food  habits  of  the  infusoria  are  among  the  most  interesting  of 
their  activities  to  the  student  of  animal  behavior.  As  to  their  food  habits, 
we  can  with  Maupas  (1889)  divide  the  infusoria  into  two  classes.  The 
first  includes  those  that  bring  the  food  to  the  mouth  by  means  of  a 
vortex  produced  by  the  peristomal  cilia ;  the  second  those  that  go  about 
in  search  of  food,  seizing  upon  it  with  the  mouth,  like  a  beast  of  prey. 
The  former  live  chiefly  upon  minute  objects,  the  latter  upon  larger  or- 
ganisms. There  is,  of  course,  no  sharp  distinction  between  the  two 
classes.  Most  of  the  infusoria  with  strong  vortices  move  about  more  or 
less  in  search  of  food,  and  most  of  those  that  seize  upon  their  prey  after 
a  search  are  aided  by  a  more  or  less  pronounced  vortex.  Thus  the 
roving  or  searching  movements  and  the  vortex  are  factors  common 
to  the  food  habits  of  most  of  the  infusoria.  The  positive  contact  re- 
action further  plays  a  most  important  part  in  obtaining  food. 

Those  species  that  depend  primarily  upon  the  ciliary  vortex  for 
obtaining  food  usually  feed  upon  bacteria  and  other  minute  organisms 
and  upon  finely  divided  organic  matter,  —  bits  of  decaying  plant  or 
animal  material.  Of  this  class  of  organisms  Paramecium  and  Stentor 
are  types.  In  some,  as  in  Paramecium,  the  food  is  limited  to  most 
minute  bodies,  such  as  bacteria  and  small  algae.  Stentor  and  others 
may  take  larger  objects.  Other  infusoria  and  even  rotifers  of  a  con- 
siderable size  are  often  seen  embedded  in  the  internal  protoplasm  of 
Stentor.  Such  animals  are  caught  in  the  strong  ciliary  vortex,  carried 
to  the  buccal  pouch,  which  often  contracts  in  such  a  way  as  to  prevent 
their  escape,  and  are  then  taken  through  the  mouth  into  the  internal 
protoplasm. 

How  do  these  organisms  succeed  in  getting  the  food  that  is  fitted  for 
them  ?  Is  there  a  selection  of  food,  and  how  is  it  brought  about  ?  Much 
of  the  difficulty  as  to  the  selection  of  food  is  solved  by  the  conditions 
under  which  these  animals  usually  live.     They  are  found  as  a  rule  in 


BEHAVIOR    UNDER   NATURAL   CONDITIONS  183 

water  which  contains  decaying  vegetable  or  animal  matter,  and  therefore 
swarms  with  bacteria.  Hence  the  usually  ciliary  current  brings  food 
continuously,  and  little  selection  is  necessary.  The  animals  take, 
within  wide  limits,  all  that  the  ciliary  current  brings.  Bits  of  scot, 
India  ink,  carmine  or  indigo,  chalk  granules,  and  the  like  are  swallowed 
along  with  the  bacteria,  though  of  course  they  are  useless  as  food.  They 
are  merely  passed  through  the  body  and  ejected  along  with  the  indi- 
gestible remains  of  the  food.  They  do  no  harm,  and  the  animal  may 
continue  to  take  them  indefinitely,  provided  it  receives  in  addition  a  suffi- 
cient amount  of  real  food.  If  the  ciliary  currents  do  not  bring  food, 
of  course  the  organisms  die  after  a  time.  It  is  well  known  that  infusoria 
appear  suddenly  in  immense  numbers,  or  disappear  with  equal  rapidity, 
according  as  the  conditions  are  favorable  or  unfavorable. 

But  the  animals  do  determine  for  themselves,  to  a  certain  extent, 
what  things  they  shall  take  as  food,  and  what  they  shall  not.  This  is 
not  done,  so  far  as  can  be  observed,  by  a  sorting  over  of  the  food  by  the 
cilia,  as  the  water  current  carries  it  to  the  mouth.  It  is  true  that  not 
all  the  particles  in  the  vortex  produced  by  the  cilia  pass  into  the  mouth. 
But  this  is  due  to  the  simple  mechanical  conditions.  The  vortex  is 
very  extensive,  and  the  mouth  is  very  small,  so  that  only  a  fraction  of  the 
water  in  the  vortex  can  ever  reach  the  mouth.  Hence  inevitably  a 
large  share  of  the  particles  in  the  vortex  are  whirled  away.  But  this  is 
true  of  particles  which  are  valuable  for  food  as  well  as  of  those  which  are 
not.  If  Stentor  is  placed  in  water  containing  immense  numbers  of  small 
algal  cells  which  are  useful  as  food,  it  is  found  that  as  many  of  these  pass 
through  the  vortex  without  being  taken  as  happens  in  the  case  of  worthless 
particles  of  soot  or  carmine. 

Choice  of  food  occurs  in  a  somewhat  cruder  fashion  than  through  a 
sorting  of  the  individual  particles  by  the  cilia.  It  takes  place  through 
the  reaction  with  which  we  have  become  familiar  in  studving  the  behavior 
of  the  organisms  under  various  stimuli.  Thus  in  Paramecium  the  re- 
jection of  unsuitable  food  takes  place  through  the  avoiding  reaction.  If 
the  ciliary  current  brings  water  containing  various  chemicals  in  solution, 
or  if  large  solid  objects  are  brought  to  the  mouth,  or  too  great  a  mass 
of  smaller  particles,  the  Paramecium  shifts  its  position  in  the  usual  way. 
It  backs  more  or  less,  turns  toward  the  aboral  side,  and  moves  to  another 
place.  The  avoiding  reaction  is  in  itself  always  an  expression  of  choice, 
in  so  far  as  it  determines  the  rejection  of  certain  conditions  of  existence. 
In  Stentor  and  Vorticella  choice  of  food  occurs  in  a  similar  manner, 
though  in  these  fixed  infusoria  there  is,  as  we  have  seen,  usually  more 
than  one  way  of  rejecting  unsuitable  conditions. 

In  Stentor  the  following  behavior  is  at  times  observed.     The  animal 


1 84  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

is  outstretched  and  feeding  quietly  in  the  usual  way.  Many  small 
objects  pass  into  the  buccal  pouch  and  are  ingested.  Suddenly  a  larger, 
hard-armored  infusorian,  Coleps,  is  drawn  into  the  pouch.  At  once 
the  ciliary  current  is  reversed  and  the  Coleps  is  driven  out  again.  Then 
the  current  is  resumed  in  the  usual  direction.  Vorticella  and  other  fixed 
infusoria  often  reject  large  objects  in  the  same  way.  But  besides  re- 
versing the  ciliary  current,  these  organisms  may,  when  the  ciliary  current 
brings  unsuitable  material,  bend  over  into  a  new  position,  contract, 
or  leave  their  place  of  attachment  and  swim  away.  All  these  reactions 
have  been  described  in  detail  in  our  account  of  the  behavior  of  Stentor. 

Thus  the  choice  of  food  in  all  these  organisms  depends  merely  upon 
whether  the  usual  negative  or  avoiding  reactions  are  or  are  not  given. 
The  avoiding  reaction  is  the  expression  of  such  choice  as  occurs.  Look- 
ing at  the  matter  from  this  standpoint,  we  are  forced  to  conclude  that  the 
entire  behavior  involves  choice  in  almost  every  detail.  The  animals, 
as  we  have  seen,  are  giving  the  avoiding  reaction  in  a  certain  degree, 
from  a  slight  widening  of  the  spiral  course  to  the  powerful  backward 
swimming,  almost  continuously.  The  straightforward  course  is  the 
expression  of  positive  choice  or  acceptance;  the  avoiding  reacting  of 
negative  choice  or  rejection.  No  distinction  can  be  made  between  choice 
and  the  usual  behavior.  Indeed,  choice  is  the  essential  principle  of 
behavior  based  on  the  method  of  trial. 

What  happens  if  the  organisms  settle  down  and  attach  themselves 
in  a  region  where  no  food  exists  ?  This  question  seems  not  to  have  been 
specially  investigated.  But  it  is  known  that  under  most  kinds  of  un- 
favorable conditions,  —  conditions  which  interfere  with  the  normal 
functions,  — the  animal,  after  a  time,  leaves  its  place  and  swims  away 
to  a  new  location.     Doubtless  this  happens  also  when  food  is  lacking. 

We  may  sum  up  the  food  habits  of  this  first  class  of  ciUates  as  fol- 
lows :  They  settle  down  in  a  certain  region  and  then  bring  a  current 
of  water  to  the  mouth.  The  particles  in  this  current  are  taken  as  food, 
without  any  sorting,  so  that  many  that  are  not  useful  are  ingested  along 
with  the  others.  But  if  decidedly  unsuitable  material  is  brought,  then 
the  animal  reacts  as  to  other  unfavorable  stimuli  —  reversing  the  cur- 
rent, contracting,  shifting  position,  or  finally  moving  away  to  a  new  place. 
The  method  of  trial  of  varied  movements  is  at  the  basis  of  the  behavior 
here  as  elsewhere. 

The  second  class  of  ciliates  includes  those  which  move  about  in  search 
of  their  food,  preying  upon  larger  organisms  and  seizing  them  with  the 
mouth.  Maupas  has  well  called  these  the  hunter  ciliates.  The  method 
of  taking  food  in  these  animals  often  resembles  in  many  respects  that  of 
the  species  already  described.      Thus  Stylonychia  runs  about  here  and 


BEHAVIOR   UNDER   NATURAL   CONDITIONS  185 

there,  producing  a  strong  vortex  leading  to  its  mouth.  This  often  carries 
other  infusoria,  of  considerable  size,  to  the  mouth.  These  are  then 
seized  and  worked  gradually  back  into  the  internal  protoplasm.  Some 
species  move  about  more  rapidly  and  more  extensively,  while  the  ciliary 
vortex  is  reduced  so  that  it  is  of  little  consequence  for  food  getting.  On 
coming  in  contact  with  another  infusorian  the  latter  is  seized  by  the 
usually  armored  mouth ;  this  is  opened  widely  and  the  prey  is  swallowed. 
In  this  way  such  infusoria  often  feed  upon  other  animals  almost  or  quite 
as  large  as  themselves,  the  mouth  opening  widely  and  the  body  becoming 
greatly  distended. 

An  excellent  example  of  one  of  these  hunter  ciliates  is  furnished  by 
Didinium.  This  animal  (Fig.  113)  is  cask-shaped,  with  a  truncate 
anterior  end,  bearing  in  its  centre  the  mouth  on 
a  slight  elevation.  The  body  bears  but  two 
circles  of  cilia.  By  the  aid  of  these,  Didinium 
swims  about  rapidly,  revolving  to  the  right  on 
its  long  axis  and  frequently  changing  its  direc- 
tion. On  coming  in  contact  with  a  solid  object 
it  stops,  pushes  forward  against  the  object  the 
conical  projection  which  bears  the  mouth,  and 

.  .  ,,  .        ,  .  „,  .  Fig.  113.  —  Didinium  seiz- 

revolves  rapidly  on  its  long  axis.  The  mouth  ing  paramecium.  After  Bal- 
is armed  with  a  number  of  strong  ribs  ending  biani- 
in  points,  which  apparently  project  a  little  from  the  cone  bearing  the 
mouth.  When  pushed  forward  against  a  soft  organism,  these  points 
apparently  pierce  and  hold  it.  The  revolution  on  the  long  axis  has  the 
appearance  of  a  process  of  boring  into  the  body.  The  mouth  now  opens 
widely  and  swallows  the  prey.  Paramecium  often  falls  a  victim  to 
Didinium  in  this  way  (Fig.  113).  Sometimes  the  Didinium  is  smaller 
than  its  prey,  forming  after  the  feeding  process  a  mere  sac  over  its 
surface. 

The  point  which  interests  us  at  present  is  that  Didinium  reacts  in 
the  way  described  not  merely  to  objects  which  may  serve  as  food,  but 
also  to  all  sorts  of  solid  bodies.  In  other  words,  the  process  is  one  of  the 
trial  of  all  sorts  of  conditions.  On  coming  in  contact  with  a  solid, 
Didinium  "  tries  "  to  pierce  and  swallow  it.  If  this  succeeds,  well  and 
good;  if  it  does  not,  something  else  is  " tried."  In  a  culture  containing 
many  specimens  of  Didinium,  the  author  has  seen  dozens  of  individuals 
reacting  in  this  way  to  the  bottom  and  sides  of  the  glass  vessel,  apparently 
making  persevering  efforts  to  pierce  the  glass.  Others  "try"  water 
plants,  or  masses  of  small  algae,  about  which  many  specimens  gather  at 
times.  Of  course  they  get  no  food  in  this  way.  On  coming  in  contact 
with  each  other,  the  animals  react  in  the  same  way,  often  becoming 


1 86  BEHAVIOR    OF   THE   LOWER    ORGANISMS 

attached  to  each  other,  and  sometimes  forming  chains  of  four  or  five. 
But  they  never  succeed  in  swallowing  one  another.  They  often  try 
rotifers  in  the  same  way,  but  the  outer  integument  of  these  organisms 
is  so  tough  that  Didinium  does  not  succeed  in  piercing  it,  and  the  rotifer 
escapes.  Stentor  and  Spirostomum  are  often  fastened  upon,  but  usually 
escape,  owing  to  their  large  size,  great  activity,  and  rather  tough  outer 
covering.  The  reason  why  Paramecium  is  usually  employed  as  food 
rather  than  other  organisms  is  clearly  due  to  the  fact  that  when  the 
Didinia  try  these,  they  usually  succeed  in  piercing  and  swallowing  them, 
while  with  most  other  objects  they  fail.1 

Didinium  is  a  type  of  the  hunter  ciliates  in  this  respect.  The  process 
of  food-getting  is  throughout  these  species  one  of  trial  of  all  sorts  of  things. 
There  is  no  evidence  that  in  some  unknown  way  the  infusoria  perceive 
their  prey  at  a  distance,  nor  that  they  decide  beforehand  to  attack  certain 
objects  and  leave  others  unattached.  They  simply  "prove  all  things 
and  hold  fast  to  that  which  is  good." 

We  cannot  do  better  in  emphasizing  this  point  than  to  quote  a  por- 
tion of  the  words  of  the  veteran  investigator  Maupas,  as  given  in  Binet's 
"The  Psychic  Life  of  Micro-Organisms"  (pp.  48,  49):  — 

"These  hunter  infusoria  are  constantly  running  about  in  search  of 
prey;  but  this  constant  pursuit  is  not  directed  toward  any  one  object 
more  than  another.  They  move  rapidly  hither  and  thither,  changing 
their  direction  every  moment,  with  the  part  of  the  body  bearing  the  bat- 
tery of  trichocysts  held  in  advance.  When  chance  has  brought  them  in 
contact  with  a  victim,  they  let  fly  their  darts  2_  and  crush  it ;  at  this  point 
of  the  action  they  go  through  certain  manoeuvres  that  are  prompted 
by  a  guiding  will.  It  very  seldom  happens  that  the  shattered  victim 
remains  motionless  after  direct  collision  with  the  mouth  of  its  assailant. 
The  hunter,  accordingly,  slowly  makes  his  way  about  the  scene  of  action, 
turning  both  right  and  left  in  search  of  his  lifeless  prey.  This  search 
lasts  a  minute  at  the  most,  after  which,  if  not  successful  in  finding  his 
victim,  he  starts  off  once  more  to  the  chase  and  resumes  his  irregular 
and  roving  course.  These  hunters  have,  in  my  opinion,  no  sensory 
organ  whereby  they  are  enabled  to  determine  the  presence  of  prey  at  a 
distance;   it  is  only  by  unceasing  and  untiring  peregrinations  both  day 

1  Balbiani  (1873)  described  Didinium  as  discharging  trichocysts  from  the  mouth 
region  against  its  prey,  thus  bringing  it  down  from  a  distance.  This  account  has  not 
been  confirmed  by  other  observers,  and  the  writer  has  never  seen  anything  of  the  sort  in 
the  innumerable  cases  of  food-taking  in  Didinium  which  he  has  observed.  It  can  hardly 
be  doubted  that  the  trichocysts  represented  in  Balbiani's  figure  (our  Fig.  113)  really  come 
from  the  injured  Paramecium,  and  not  from  the  Didinium. 

2  This  use  of  the  trichocysts  has  not  been  confirmed  by  other  writers  and  was  not 
absolutely  observed  by  Maupas  himself. 


BEHAVIOR    UNDER   NATURAL   CONDITIONS  187 

and  night  that  they  succeed  in  providing  themselves  with  sustenance. 
When  prey  abounds,  the  collisions  are  frequent,  their  quest  profitable, 
and  sustenance  easy;  when  scarce,  the  encounters  are  correspondingly 
less  frequent,  the  animal  fasts  and  keeps  his  Lent.  The  Lagynus 
crassicollis,  accordingly,  never  sees  its  victim  from  a  distance  and  in  no 
case  directs  its  movements  more  toward  one  object  of  prey  than  toward 
another.  It  roams  about  at  random,  now  to  the  right  and  now  to  the 
left,  impelled  merely  by  its  predatory  instinct  —  an  instinct  developed 
by  its  peculiar  organic  construction,  which  dooms  it  to  this  incessant 
vagrancy  to  satisfy  the  requirements  of  alimentation." 

It  is  evident  that  these  words  of  Maupas  are  an  excellent  description 
of  behavior  based  on  the  general  method  of  trial  of  all  sorts  of  conditions 
though  varied  movements,  and  they  bring  out  clearly  the  essential  prin- 
ciples in  the  food  reactions  of  infusoria.  The  same  method  of  behavior 
is  found,  as  we  have  seen,  throughout  almost  the  whole  circle  of  activi- 
ties in  these  organisms ;  the  food  reactions  epitomize  the  entire  behavior. 

LITERATURE  X 

A.  Modifiability  of  behavior  in  infusoria:  Jennings,  1902,  1904  d\  Hodge  and 
Aikins.  1895. 

B.  Food  habits  of  infusoria:  Maupas,  in  Binet,  1889;  Balbiani,  1873. 


PART    II 

BEHAVIOR   OF   THE   LOWER  METAZOA 

CHAPTER    XI 
INTRODUCTION   AND   BEHAVIOR   OF   CCELENTERATA 

INTRODUCTION 

While  unicellular  forms  are  the  very  lowest  organisms,  an  account 
limited  to  their  behavior  alone  might  give  us  a  one-sided  view  of  the  prin- 
ciples of  behavior  in  the  lower  organisms.  The  Metazoa  differ  from  the 
Protozoa  structurally  in  the  important  facts  that  their  bodies  are  made 
of  many  cells  and  that  they  have  a  nervous  system.  Does  the  behavior 
of  such  organisms  differ  essentially  from  that  of  the  Protozoa?  Have 
we  been  dealing  in  our  study  of  unicellular  organisms  with  a  peculiar 
group,  whose  behavior  is  of  a  character  essentially  different  from  that 
of  other  animals  ?  How  far  do  the  general  principles  to  be  deduced  from 
the  behavior  of  Protozoa  hold  for  animals  in  general  ?  To  answer  these 
questions  is  the  province  of  the  following  chapters. 

We  shall  take  up  in  detail  the  behavior  of  only  one  of  the  lowest 
groups  of  Metazoa  —  the  ccelenterates.  This  will  be  followed  by  a 
chapter  on  some  of  the  main  features  of  behavior  in  other  invertebrates. 
A  general  analysis  of  behavior  in  both  Protozoa  and  the  lower  Metazoa 
is  found  in  the  third  part  of  the  book. 

BEHAVIOR   OF   CCELENTERATA 

The  Ccelenterata  or  Cnidaria  form,  perhaps,  the  lowest  of  the  larger 
groups  of  Metazoa.  This  group  includes  the  fresh-water  Hydra, 
hydroids,  sea  anemones,  corals,  and  jellyfishes  or  medusae.  The 
behavior  of  the  corals  and  of  hydroids  has  been  comparatively  little 
studied,  so  that  the  present  account  will  be  limited  mainly  to  Hydra,  the 
sea  anemones,  and  medusae. 

All  of  these  animals  are  made  up  of  many  cells,  of  many  different 
kinds,  and  usually  arranged  in  three  more  or  less  irregular  layers.     Of 

1 88 


BEHAVIOR   OF   CCELENTERATA  189 

special  interest  from  the  standpoint  of  behavior  are  the  nerve  cells.  In 
Hydra  these  consist  of  comparatively  few,  small  cells  with  long,  branched 
processes,  scattered  among  the  ectoderm  and  entoderm  cells.  They 
apparently  serve  to  connect  the  other  cells.  In  the  sea  anemones  the 
nerve  cells  are  more  numerous  than  in  Hydra,  but  are  likewise  scattered 
throughout  the  body,  in  both  ectoderm  and  entoderm.  They  are  some- 
what more  numerous  in  the  neighborhood  of  the  mouth  than  elsewhere. 
In  Medusae  the  nervous  system  is  more  concentrated.  The  cells  and 
fibres  form  two  rings  about  the  edge  of  the  body :  one  lies  just  beneath 
the  ectoderm  of  the  exumbrella,  the  other  beneath  that  of  the  subum- 
brella.  These  rings  are  interconnected  by  scattered  fibres.  A  plexus 
of  nerve  fibres  covers  the  entire  concave  surface  of  the  subumbrella 
and  manubrium,  beneath  the  ectoderm.  This  plexus  is  compared  by 
Romanes  as  regards  texture  to  a  sheet  of  muslin.  Nerve  cells  and  fibres 
are  found  also  in  the  tentacles,  but  are  not  known  on  the  convex  surface 
of  the  exumbrella.  The  two  marginal  nerve  rings  are  often  spoken  of 
as  the  "central  nervous  system"  in  medusae. 

1.    Action  System.    Spontaneous  Activities 

In  the  ccelenterates  we  take  up  animals  with  action  systems  differing 
much  from  those  of  the  organisms  we  have  hitherto  studied.  The  chief 
movements  are  due  to  contractions  and  extensions  of  parts  of  the  body 
and  tentacles,  produced  by  contractions  of  the  muscle  fibres.  The  body 
is  flexible,  and  being  radially  symmetrical  may  contract  or  bend  with 
equal  ease  in  any  direction. 

Under  natural  conditions,  Hydra  and  the  sea  anemone  are  usually 
attached  and  at  rest,  while  the  medusa  may  be  in  movement.  Let  us  ex- 
amine the  behavior  under  such  conditions,  when  no  observable  stimulus 
is  acting  on  them,  aside  from  the  usual  conditions  of  existence. 

If  we  observe  an  undisturbed  green  Hydra  attached  to  a  water  plant 
or  the  side  of  a  glass  vessel,  we  find  that  it  usually  does  not  remain  still, 
but  keeps  up  a  sort  of  rhythmic  activity.  After  remaining  in  a  certain 
position  for  a  short  time  it  contracts,  then  bends  to  a  new  position,  and 
reextends  (Fig.  114).  In  this  new  position  it  remains  for  one  or  two 
minutes,  then  it  again  contracts,  changes  its  position,  and  again  extends. 
This  continues,  the  changes  of  position  occurring  every  one  or  two  min- 
utes. In  this  way  the  animal  thoroughly  explores  the  region  about  its 
place  of  attachment  and  largely  increases  its  chances  of  obtaining  food. 
This  motion  seems  to  take  place  more  frequently  in  hungry  individuals, 
while  in  well-fed  specimens  it  may  not  occur. 

Thus  contractions  take  place  without  any  present  outward  stimulus ; 


190 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


the  movements  are  due  to  internal  changes  of  some  sort,  like  those  of 
Vorticella.     The  same  behavior  may  be  produced,  as  we  shall  see  later, 

by  external  stimuli. 
In  the  yellow  Hy- 
dra such  move- 
ments do  not  occur 
—  at  least  not  with 
such  frequency. 


Fig.  114.  —  Spontaneous  changes  of  positions  in  an  undis- 
turbed Hydra.  Side  view.  The  extended  animal  (1)  contracts 
(2),  bends  to  a  new  position  (3),  and  then  extends  (4). 


Fig.  115.  —  Dia- 
gram of  different  posi- 
tions taken  by  Hydra,  as 
seen  from  above.  After 
Wagner. 


This  is  apparently  correlated  with  the  fact  that  the  yellow  Hydra  has 
very  long  tentacles,  which  lie  in  coils  all  about  it,  so  that  exploratory 
movements  are  not  necessary  in  order  to  reach  such  food  as  may  be 

found  in  the  neighborhood. 

If  a  green  Hydra  is  left  for  long 
periods  undisturbed,  it  does  not 
remain  attached  in  the  same  posi- 
1  tion,  but  moves  about  from  place 
to  place.  The  movements  often 
take  place  in  random  directions,  — 
the  animal  starting  first  in  one  direc- 
tion, then  in  another.  Figure  116 
shows  the  movements  of  a  green 
Hydra,  which  was  left  alone  for  some 
days  in  the  bottom  of  a  large,  clean 
glass  dish,  the  light  coming  from  a 
window  at  the  right.  This  move- 
ment is  probably  brought  about  by 
Fig.  n6. -Path  followed  by  a  green  hunger  —  the  animals  taking  a  new 

Hydra  that  was  left  for  some  days  undisturbed  position  when  food  becomes  Scarce. 
on   the   bottom  of  a  clean  glass  dish.     After    £L     ,  .  .  1 

Wagner  (1905).  Hydra  may  move   about   in   several 


BEHAVIOR  OF   CCELENTERATA 


191 


different  ways.  In  the  commonest  method  the  animal  places  its  free 
end  against  the  substratum,  releases  its  foot,  draws  the  latter  forward, 
reattaches  it,  and  repeats  the  process,  thus  looping  along  like  a  measur- 
ing worm  (Fig.  117).  In  other  cases  it  attaches  itself  by  its  ten- 
tacles, releases  its  foot,  and 
uses  the  tentacles  like  legs. 
A  still  different  form  of  loco- 
motion has  been  described, 
in  which  the  animal  is  said 
to  glide  along  on  its  foot; 
how  this  is  brought  about  is 
not  known. 

In  sea  anemones,  rhyth- 
mical contractions  of  the  un- 
disturbed animal  have  ap- 
parently not  been  described. 
But  Loeb  (1891,  p.  59)  finds 
that  Cerianthus  if  not  fed 
will  after  a  time  leave  its 
place  in  the  sand  and  creep 
about,  finally  establishing 
itself  in  a  new  place.  The 
common  sea  anemone  Me- 
tridium  moves  about  fre- 
quently from  place  to  place 
on  the  sides  or  bottom  of  the 
aquarium,  and  so  far  as  can 
be  observed,  this  seems  often 
due  simply  to  hunger  or  other 

.  1  1...  •,  Fig.    117.  —  Hydra    looping    along    like  a  leech, 

internal  Conditions ;  It  OCCUrS  Mter  Wagner  (1905).     1-6,  Successive  positions. 

under     apparently     uniform 

external  conditions.  A  common  method  of  movement  in  sea  anemones 
is  to  glide  about  on  the  foot,  —  the  lower  surface  of  the  foot  sending 
out  extensions  and  moving  in  a  manner  similar  to  that  of  the  foot  of 
mollusks.     There  are  doubtless  other  methods  of  locomotion. 

The  spontaneous  contraction  and  change  of  position  which  plays  a 
subordinate  part  in  fixed  forms  has  become  the  rule  in  medusae.  They 
are  commonly  found  swimming  about  by  means  of  rhythmical  contrac- 
tions. Since  there  are  no  corresponding  changes  in  external  condi- 
tions, these  contractions  must  be  due  to  internal  changes.  The 
internal  changes  need  not  of  course  be  themselves  of  a  rhythmical 
character.     They  may  take  place  steadily,  inducing  a  contraction  only 


192 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


when  a  result  of  a  certain  intensity  has  been  reached  (see  Loeb,  1900, 
p.  21). 

In  the  small  medusa  Gonionemus  there  is  under  natural  conditions  a 
cycle  of  activity  that  is  of  great  interest;  it  has  been  well  described  by 
Yerkes  (1902,  a  and  b,  1903,  1904)  and  Perkins  (1903).  At  times  the 
animal  is  found  attached  by  certain  adhesive  pads  on  its  tentacles  to 


Fig.  118.  —  Young  Gonionemus  resting  on  the  bottom,  with  the  opening  of  the  bell  upward. 
After  Perkins  (1903). 

the  vegetation  of  the  bottom  or  to  other  surfaces  (Fig.  118).  Leaving 
its  attachment,  it  swims  upward  to  the  upper  surface  of  the  water,  the 
convex  surface  of  the  bell  being  upward,  and  the  tentacles  contracted 
(Fig.  119).  Reaching  the  upper  surface  it  turns  over 
"  and  floats  downward  with  bell  relaxed  and  inverted, 
and  tentacles  extending  far  out  horizontally  in  a  wide 
snare  of  stinging  threads  which  carries  certain  destruc- 
tion to  creatures  even  larger  than  the  jellyfish  itself 
(Fig.  120)"  (Perkins,  1903,  p.  753).  Reaching  the 
bottom,  it  swims  again  to  the  top  and  repeats  the 
process.  It  may  thus  continue  this  process  of  "  fish- 
ing," as  Perkins  calls  it,  all  day  long.  It  is  chiefly  in 
this  way  that  it  captures  its  food. 
This  cycle  of  spontaneous  activities  is  in  some  respects  similar  to 
that  of  the  green  Hydra  described  above,  though  much  more  complex. 
Both  illustrate  the  fact  that  complex  movements  and  changes  of  move- 
ment may  occur  from  internal  causes,  without  any  change  in  the  environ- 
ment. 


Fig  .  1  1  g  .  — ■ 
Gonionemus  swim- 
ming upward  with 
contracted  tentacles. 
After  Perkins  (1903). 


2.     Conditions 


required     for    retaining    a 
Righting    Reactions,    etc. 


Given     Position  ; 


Hydra  and  the  sea  anemones  tend  to  retain  a  certain  position;  we 
usually  find  them  at  rest  with  foot  attached  and  head  free.  This  usual 
position  is  often  said  to  be  due  to  a  reaction  to  gravity  or  to  contact,  or 


BEHAVIOR   OF   CCELENTERATA 


193 


to  some  other  simple  stimulus.  It  will  be  found  instructive  to  examine 
the  different  conditions  on  which  depends  whether  the  animal  shall  or 
shall  not  retain  a  given  position  in  which  it  finds  itself.  It  will  be  found 
that  the  matter  is  not  an  entirely 
simple  one. 

Let  us  take  first  the  case  of  Hydra. 
Suppose  the  animal  to  be  placed  on  a 
horizontal  surface  with  head  down- 
ward and  foot  upward.  It  does  not 
retain  this  position,  but  bends  the 
body,  placing  the  foot  against  the 
bottom,  releases  its  head,  and 
straightens  upward.  This  is  what 
is  commonly  called  the  "righting" 
reaction.  In  Hydra  it  is  not  due  to 
a  tendency  to  keep  the  body  in  a  cer- 
tain position  with  reference  to  gravity, 
for  the  animal  may  remain  attached 
to  the  bottom,  with  head  projecting 
upward,  or  to  the  surface  film,  with 
head  projecting  downward,  or  to  a 
perpendicular  surface,  with  the  body 
transverse  or  oblique  to  the  direction 
of  gravity.  There  is  even  apparently 
a  certain  tendency  to  direct  the  head 
downward.  Thus  out  of  100  green 
Hydras  attached  to  a  perpendicular 
surface,  96  had  the  head  lower  than 
the  foot,  3  were  horizontal,  and  1  had 
the  head  directed  upward.  It  is  thus 
clear  that  the  righting  reaction  of  a 
Hydra  which  has  been  inverted  on 
the  bottom  cannot  be  due  to  any 
unusual  relation  to  the  direction  of 
gravity. 

To  what,  then,  is  the  reaction 
due  ?  Evidently  there  is  a  tendency  to 
keep  the  foot  in  contact  with  a  surface,  for  the  body  is  bent  till  the  foot 
comes  in  contact.  But  this  is  not  all ;  the  reaction  does  not  stop  at  this 
point.  There  is  likewise  a  tendency  to  keep  the  head  free,  for  it  is  re- 
leased. But  still  this  is  not  all,  for  now  the  body  is  straightened ;  then 
the  tentacles  are  spread  out  symmetrically  in  various  directions. 


194 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


It  is  clear  that  the  reaction  is  directed  toward  getting  the  organism 
into  its  usual  position,  which  might  perhaps  be  called  the  "normal"  one; 
this  normal  position  has  various  factors,  —  attachment  of  foot,  freedom 
of  head,  comparative  straightness  of  the  body,  and  tentacles  outspread. 

This  is,  of  course,  exactly  the 
position  which  is  most  favorable 
for  obtaining  food. 

Suppose  now  that  our  Hydra 
has  reached  this  position,  and 
all  the  conditions  remain  con- 
stant ;  is  this  sufficient  ?  We 
find  that  it  is  not.  If  the  con- 
ditions remain  so  constant  that 
no  food  is  obtained,  the  Hvdra 
becomes  restless  and  changes  the 
position  of  its  body  repeatedly, 
though  still  retaining  its  attach- 
ment by  the  foot.  But  later 
even  this  is  given  up,  and  the 
animal,  of  its  own  internal  im- 
pulse, quite  reverses  the  position 
attained  through  the  "righting 
reaction."  It  now  bends  its 
body,  attaches  its  head,  and  re- 
leases its  foot,  thus  bringing  it 
back  into  the  inverted  position. 
Is  this  because  the  irritability 

Fig.  121.—  Process  by  which  Cerianthus  rights  of  nead  ail  1  foot  have  become 
itself  when  inverted  in  a  tube.  The  figures  are  taken  reversed,  SO  that  the  head  now 
at  intervals  during  the  course  of  one  hour.     After  ,  .  ,       ,        , 

Loeb  (1891).  tends    to    remain    attached,   the 

foot  free?  Apparently  not,  for 
no  sooner  has  the  organism  taken  the  inverted  position  than  it  draws 
its  foot  forward  and  now  performs  the  "righting  reaction"  again,  so  that 
it  stands  once  more  on  its  foot.  These  alternations  of  behavior  are 
repeated,  and  we  find  that  by  this  means  the  animal  is  moving  from 
place  to  place,  as  in  Fig.  117. 

It  seems  clearly  impossible  to  refer  each  of  these  acts  or  the  whole 
behavior  to  any  particular  present  external  stimulus.  Through  hunger 
the  Hydra  is  driven  to  move  to  another  region,  and  these  different  oppo- 
site acts  are  the  means  by  which  another  region  is  reached.  Each  step 
in  the  behavior  is  partly  determined  by  the  preceding  step,  partly  by 
the  general  condition  of  hunger.     The  same  behavior  is  often  seen^  as 


BEHAVIOR   OF   CCELENTERATA 


195 


xz 


.v^ 


& 


mi 


•Ml 


//Syr-l 


we  shall  see  later,  under  continued  injurious  stimulation  of  different 
kinds. 

In  speaking  of  righting  reactions,  it  is  often  said  that  the  organism 
is  forced  by  the  different  irrita- 
bilities of  diverse  parts  of  the 
bodv  to  take  a  certain  orienta- 
tion  with  reference  to  gravity 
or   to    the   surface  of   contact 
(see,  for  example,  Loeb,  1900,    4mToHH^ 
p.     184).        The    facts      just  MMMiM$ 
brought  out  show  that  we  can 
in  Hydra  consider  this  orienta- 
tion forced  only  in  the  general 
sense    that    all    things  which 
occur     may     be      considered 
forced.     Man  takes  sometimes 
a  sitting  position,  sometimes  a        FlG.  I22.-_Pos;tion  taken  by  Cerianthus  after  it 

Standing  one,  Sometimes    a    re-  nas  been  placed  on  its  side  on  a  wire  mesh.    After  Loeb. 

clining   one,   depending   upon  ' 

his  "physiological  state"  and  past  history,  and  the  facts  are  quite 
parallel  for  Hydra.  So  far  as  objective  evidence  shows,  the  behavior  is 
not  forced  in  Hydra  in  any  other  sense  than  it  is  in  man.     The  animal 

takes  that  position  which  seems  best  adapted  to 
the  requirements  of  its  physiological  processes; 
these  requirements  vary  from  time  to  time. 

In  the  sea  anemone  Cerianthus  the  conditions 
for  retaining  a  certain  position  are  somewhat  more 
complex  than-  in  Hydra,  according  to  the  account 
given   by  Loeb  (1891).     The   animal  is  usually 
Fig.    123.  — Cerianthus  found  in  an  upright  position,  occupying  a  mucus- 

which  has  woven  itself  through   ..        .         .         .         ,  ,        T1.       .  ,     .  ,     , 

a  meshwork,  as  a  result  of  re-  hned  tube  in  the  sand.  If  placed  head  down- 
peatediy  inverting  the  latter.  warcj  in  a  test-tube,  it  rights  itself  in  the  same 

After  Loeb  (1S91).  TT     .  .  . °       .         .      .     .  . 

way  as  Hydra,  freeing  the  head,  bringing  the 
foot  into  contact,  and  straightening  the  body  (Fig.  121).  But  in  this 
animal,  gravity  clearly  plays  a  part  in  the  behavior.  Loeb  placed  the 
animal  on  its  side  on  a  wire  screen  of  large  mesh.  Thereupon  it  bends 
its  foot  down  through  the  meshes,  lifts  up  its  head,  and  takes  its  usual 
position  in  line  with  gravity  (Fig.  122).  If  now  the  screen  is  turned 
over,  the  animal  again  directs  its  head  upward,  its  foot  downward  —  as 
a  human  being  under  similar  circumstances  would  do  if  possible.  It 
may  thus  weave  itself  in  and  out  through  the  meshes  (Fig.  123). 

But  to  be  in  line  with  gravity,  with  head  free,  is  not  the  only  require- 


196  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

ment  for  Cerianthus.  Loeb  found  that  it  would  not  remain  indefinitely 
in  this  position  on  the  wire  screen,  as  it  does  in  the  sand.  After  a  day  or 
so  it  pulls  its  foot  out  of  the  wire  and  seeks  a  new  abode.  Only  when  it 
can  get  the  surface  of  its  body  in  contact  with  something,  as  is  the  case 
when  it  is  embedded  in  the  sand  in  its  natural  habitat,  is  it  at  rest.  If 
this  condition  is  fulfilled,  the  requirement  of  the  usual  position  in  line 
with  gravity  may  be  neglected.  Loeb  found  that  when  the  animal  is 
placed  in  a  test-tube,  so  that  its  body  is  in  contact  with  the  sides,  it  re- 
mains here  indefinitely,  even  though  the  tube  is  placed  in  a  horizontal 
position  (Loeb,  1891,  p.  54).  The  head  is  bent  upward,  but  the  body 
remains  transverse  to  the  direction  of  gravity.  Similarly,  the  anemone 
Sagartia  may  ofttimes  take  a  position  on  the  surface  film  with  head 
down,  although  usually  it  maintains  an  upright  position  (Torrey,  1904). 

But  even  the  usual  position  in  line  with  gravity,  and  with  sides  in 
contact,  does  not  satisfy  Cerianthus  indefinitely,  if  left  quite  undisturbed. 
If  it  secures  no  food,  it  again  leaves  its  place  and  seeks  another  region. 

Thus  that  the  animal  may  remain  quiet  in  a  given  position  a  consid- 
erable number  of  conditions  should  be  fulfilled,  constituting  altogether 
what  we  may  call  the  "normal"  state  of  the  animal.  The  conditions  are 
the  following:  (1)  the  foot  should  be  in  contact;  (2)  the  head  should 
be  free;  (3)  the  body  should  be  straight;  (4)  the  axis  of  the  body  should 
be  in  line  with  gravity,  with  the  head  above;  (5)  the  general  body  sur- 
face should  be  in  contact ;    (6)  food  should  be  received  at  intervals. 

If  these  conditions  are  largely  unfulfilled,  the  animal  becomes  rest- 
less, moves  about,  and  finds  a  new  position.  But  no  one  of  these  condi- 
tions is  an  absolute  requirement  at  all  times,  unless  it  be  that  of  having 
the  head  free.  In  the  wire  screen  (Fig.  122)  the  animal  remains  for  a 
day  or  so  if  in  the  required  position  with  reference  to  gravity,  even 
though  foot  and  body  surface  are  not  in  contact.  In  the  horizontal  test- 
tube  it  remains  with  foot  and  surface  in  contact,  though  the  body  is  not 
straight  nor  in  line  with  gravity.  If  all  conditions  are  fulfilled  save  that 
of  food,  the  animal  remains  for  a  time,  then  finally  moves  away. 

Clearly,  the  holding  of  any  given  position  depends,  not  on  the  rela- 
tion of  the  body  to  any  one  or  two  sources  of  stimulation,  but  on  the 
proper  maintenance  of  the  natural  physiological  processes  of  the  organ- 
ism. The  animal  does  not  always  maintain  a  certain  position  with  rela- 
tion to  gravity,  nor  does  it  always  keep  its  body  straight,  nor  its  foot  in 
contact,  nor  its  body  surface  in  contact.  It  does  not  at  all  times  receive 
food.  It  may  remain  for  considerable  periods  with  one  or  more  condi- 
tions lacking.  It  tends  on  the  whole  to  take  such  a  position  as  is  most 
favorable  to  the  unimpeded  course  of  the  normal  physiological  processes. 
Certain  usually  required  conditions  may  be  dispensed  with,  provided 


BEHAVIOR   OF   CCELENTERATA  197 

other  favorable  ones  are  present.  The  behavior  represents  a  compro- 
mise of  the  various  needs  imposed  upon  the  animal  by  its  physiological 
processes. 

In  the  sea  anemone  Antholoba  reticulata,  according  to  Burger  (1903), 
the  requirements  for  retaining  a  given  position  are  extraordinary.  This 
animal  is  usually  found  attached  to  the  backs  of  crabs ;  it  is  thus  carried 
about,  and  finds  much  opportunity  for  obtaining  nourishment.  If  re- 
moved from  the  crab's  back,  the  animals  attach  themselves  to  the  stony 
bottom  and  spread  the  tentacles.  But  after  four  or  five  days  they  re- 
lease their  hold  on  the  bottom  and  invert  themselves,  directing  the  foot 
upward.  Now  when  a  crab's  limb  comes  in  contact  with  the  foot,  the 
latter  attaches  itself  and  folds  about  the  limb,  so  that  the  anemone  is 
dragged  about  by  the  crab.  It  now,  in  the  course  of  several  hours, 
climbs  up  the  crab's  leg  to  its  back,  where  it  establishes  itself.  The  sea 
anemone  thus  by  its  own  activity  attains  the  extraordinary  situation 
where  it  is  usually  found.  The  whole  train  of  action  is  like  that  shown 
in  the  complicated  and  adaptive  instincts  of  higher  animals. 

3.     General  Reaction  to  Intense  Stimuli 

The  most  characteristic  reaction  of  the  ccelenterates  to  intense  stimuli 
of  all  sorts  is  a  contraction  of  the  whole  body.  In  Hydra  and  the  sea 
anemones  the  body  is  thus  shortened  and  thickened,  becoming  more 
nearly  spherical.  The  animals  thus  shrink  close  to  the  substratum 
and  present  less  surface  than  before  to  the  stimulating  agent.  In  the 
medusae  the  sudden  contraction  of  course  carries  the  animal  away  from 
the  stimulating  object.  The  first  contraction  is  usually  repeated  many 
times,  thus  inaugurating  a  period  of  swimming  by  which  the  animal  may 
be  widely  removed  from  the  stimulus.  Such  contractions  occur  in  re- 
sponse both  to  general  stimulation  and  to  local  stimulation,  if  the  latter 
is  very  intense. 

Under  most  circumstances  the  contraction  of  Hydra  or  the  sea  anem- 
one of  course  tends  to  remove  the  organism  from  any  source  of  danger, 
rendering  it  for  example  less  likely  to  be  seized  by  a  predatory  animal. 
But  the  reaction  takes  place  in  the  same  way  under  circumstances  in 
which  it  is  of  no  defensive  value.  If  the  foot  of  the  attached  Hydra 
is  strongly  stimulated,  the  animal  contracts  as  usual ;  the  contraction  is 
then  of  course  toward  the  source  of  stimulation,  not  away  from  it.  If 
the  entire  vessel  containing  the  animals  is  heated  to  30  degrees,  the 
Hydras  contract,  though  this  of  course  does  not  tend  to  remove  them 
from  the  high  temperature.  It  is  clear  that  for  all  sorts  of  stimuli  that 
are  unfavorable  these  animals  have  a  certain  reaction  which  is  usually 


io8 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


regulatory  (beneficial) ;  they  give  this  reaction  whatever  the  nature  of 
the  unfavorable  stimulus,  even  under  circumstances  where  it  is  not 
regulatory.  This  is  an  illustration  of  a  characteristic  general  trait  of 
behavior  in  lower  animals ;  their  reactions  are  commonly  not  specific, 
but  general  in  character.  As  we  shall  see  later,  this  contraction  is  not 
the  final  recourse  of  the  stimulated  ccelenterate.  If  stimulation  con- 
tinues, the  animal  usually  sets  in  operation  other  activities,  which  remove 
it  from  the  stimulating  agent. 


4.   Localized  Reactions 

Hydra.  —  In  Hydra,  intense  stimuli  restricted  to  a  small  spot  on 
the  body  or  a  tentacle  usually  produce  contraction  at  that  point,  some- 
times spreading  much  or 
little,  sometimes  not  at  all. 
This  reaction  is  produced  by 
many  sorts  of  stimuli.  If 
the  contraction  remains  pre- 
cisely localized,  as  it  some- 
times does,  the  body  or 
tentacle  bends  sharply  at 
the  point  stimulated. 

A      precisely      localized 
chemical     stimulus    is    pro- 
duced in  the  following  way. 
.    ,      .    ,     ,     7 ,  A  fine  capillary  glass  rod  is 

Fig.  124. — A  chemical  (ch.)  is  brought  against  a                                      1  •  • 

certain  spot  on  one  side  of   a  Hydra  (a).     Thereupon  dampened  and  its      tip     IS 

this  spot  contracts,  bending  the  Hydra  toward  the  side  dipped     in  SOme  powdered 

stimulated  (b).  1  1    .  _F 

chemical.  Methylene  blue 
or  methyl  green  is  convenient  to  use,  since  the  distribution  of  4he  chemi- 
cal in  the  water  is  easily  seen  by  means  of  the  color.  The  point  of  this 
fine  rod,  covered  with  the  chemical,  is  brought  close  to  the  body  of  a 
Hydra.  The  chemical  diffuses  and  reaches  a  small  area  on  the  body. 
Local  stimulation  by  heat  may  be  produced  with  the  simple  apparatus 
devised  by  Mast  (1903).  A  glass  tube  is  drawn  out  at  its  middle  to 
capillary  size,  then  bent  so  as  to  form  a  loop.  The  two  ends  are 
passed  through  a  cork  for  support,  and  to  them  are  attached  rubber 
tubes.  In  this  way  water  of  any  desired  temperature  may  be  passed 
through  the  fine  tube,  and  this  may  be  brought  close  against  the  body  of 
the  animal  at  any  desired  point. 

When  the  strong  chemical  or  the  heat  reaches  a  certain  spot  on  the 
body,  this  spot  at  once  contracts,  so  that  the  body  makes  a  knee-shaped 


BEHAVIOR   OF   CCELENTERATA 


199 


bend  at  this  point  (Fig.  124).  Such  a  bending  is  produced  by  most 
strong  chemicals;  strong  acids  placed  in  a  capillary  tube,  the  tip  of 
which  is  applied  to  the  body,  show  it  clearly.  As  a  result  of  the  bend 
the  head  of  the  animal  becomes  directed  toward  the  chemical  or  the 
heated  region,  and  is  therefore  strongly  stimulated,  so  that  the  Hydra 
now  contracts  as  a  whole.  Thus  the  result  of  the  bending  is  to  carry 
the  most  sensitive  part  of  the  animal  into  the  injurious  agent,  where  it 
is  still  further  injured.  This  reaction  is  produced  only  by  strong,  inju- 
rious agents,  and  is  really  an  incidental  result  of  the  local  injury  pro- 
duced. The  point  injured  remains  contracted  for  a  long  time  after  the 
stimulating  agent  has  ceased  to  act.  The  Hydra  may  contract  com- 
pletely, so  that  the  bend  disappears,  but  on  extension  the  bend  is  still 
found  at  the  injured  spot.  It  is  evident  that  this  bending  reaction  is 
not  a  regulatory  one,  and  it  is  apparently  never  shown  in  nature,  since 
the  conditions  necessary  for  its  production  are  practically  never  present. 
It  is  a  product  of  the  laboratory.  As  we  shall  see  later,  after  reaction 
in  this  manner,  Hydra  usually  sets  in  operation  other  reactions,  which 
do  act  in  a  regulatory  way. 

Sea  Anemones.  —  Intense  local  stimulation  of  the  column  in  the  sea 
anemones  usually  produces  a  contraction  of  the  entire  body,  or  a  move- 
ment of  tentacles  on  the  side  stimulated,  in  the  way  described  later.  In 
Sagartia  (Torrey,  1904,  p.  208),  stimulation  of  the  edge  of  the  foot 
induces  a  local  contraction  of  the  foot  and  base  of  the  column,  with 
discharge  of  acontia  —  the  defensive  weapons  of  the  animal. 

Local  stimulation  of  the  tentacles  causes  in  the  different  sea  anem- 
ones various  reactions.  Often  slight  local  stimulation  causes  the  tenta- 
cles to  wave  about ;  this  and  similar  phenomena  will  be  described  in 
connection  with  the  food  reactions.  In  most  sea  anemones  local  stimu- 
lation of  the  tentacles,  especially  if  intense,  causes  them  to  shorten  by  con- 
traction, or  to  collapse  and  become  very  slender.  This  is  followed  in 
many  cases  by  a  contraction  of  the  whole  body.  In  Aiptasia  an  immedi- 
ate contraction  of  the  entire  body  follows  even  a  slight  stimulation  of 
the  tip  of  one  of  the  long  tentacles. 

Medusa.  —  In  medusa?,  intense  stimulation  of  one  side  of  the  bell 
causes  immediate  contraction  of  that  side,  accompanied  by  a  less  marked 
contraction  of  the  remainder  of  the  bell.  The  stronger  contraction  on 
the  side  stimulated  turns  the  animal  away  from  that  side,  and  its  subse- 
quent locomotion  removes  it  at  once  from  the  stimulating  agent.  Thus 
the  appropriate  direction  of  movement  is  here  determined  in  the  sim- 
plest way  —  by  contraction  of  the  part  stimulated.  Such  effects  are 
produced  by  mechanical  and  chemical  stimulations,  by  heat,  by  elec- 
tricity, and  apparently  by  light.     In  Hydra,  as  we  have  seen,  identically 


200 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


the  same  reaction  has  the  opposite  effect,  subjecting  the  animal  still 
further  to  the  action  of  the  stimulating  agent;  other  reactions  must 
supervene  before  the  animal  is  removed  from  the  stimulus.  Intense 
stimulation  of  the  tentacles  of  the  medusa  or  of  the  margin  of  the  bell 

induces,  in  Gonionemus,  a  direct  contrac- 
tion of  the  tentacles. 

When  the  margin  or  under  surface  of 
the  medusa  bell  is  locally  stimulated,  the 
manubrium  behaves  in  a  manner  that  is 
of  great  interest.  This  has  been  described 
by  Romanes  (1885)  m  tne  medusa  Tiar op- 
sis  indicans.  If  the  margin  or  under  sur- 
face of  the  bell  is  sharply  stimulated  with 
a  needle,  the  manubrium  at  once  bends 
over  and  applies  its  tip  to  the  point  stimu- 
Fig.  125.—  The  medusa  Tiaropsis  lated  (Fig.  125).      The    reaction    is    thus 

indicans,  applying  its  manubrium  to  a  ■     i        1         t-      i  tt  1 

point  on  the  margin  which  has  been  vel7     precisely     localized.         How    does     it 

stimulated,     x,  y,  z,  cuts  made  for  happen    that    the  manubrium  is  able  to 

experimental     purposes.      After    Ro-  1  ^1^1  •  1       i  1 

manes  (1885).  locate  exactly  the  point  touched,  and  to 

bend  at  once  in  that  direction  ? 
In  answer  to  this  question,  Loeb  presents  a  very  simple  explanation, 
which  deserves  attention,  as  it  is  a  type  of  many  of  the  recent  hypotheses 
put  forward  to  explain  the  behavior  of  organisms.     According  to  Loeb, 
this  behavior  is  due  simply  to  the  spread- 
ing out  of  the  local  contraction  caused  by 
the  stimulus.      "Every  localized  stimulus 
leads  to  an  increase  in  the  muscular  tension 
on  all  sides,  which  is  most  intense  near  the 
stimulated  spot.      Now  if  we  decompose 
each  of   the  lines  of  increase  of    tension 
(aa'}  ab',  ac' ',  ad',  ae'    Fig.    126)  radiating        „  „.  .,, 

v  '       .'  .  .    .  Fig.  126.  —  Diagram  to  illustrate 

from  the  Stimulated  Spot,  into  a  meridional  Loeb's  explanation  of  the  localization 

component  aa\  dd\  bb',  etc.,  and  an  equa-  aV^i^cToo)  ^  manubrium- 
torial    component,   it   is   evident  that    the 

latter  can  have  no  influence  on  the  manubrium.  Only  the  meridional 
components  can  have  an  influence,  and  of  these  the  one  passing  through 
the  stimulated  spot  is  the  largest.  This  fact  must  necessarily  cause  a 
bending  of  the  manubrium  toward  the  stimulated  spot"  (Loeb,  1900, 

P-  32). _ 

This  explanation  represents  the  behavior  as  of  the  simplest  character 
—  a  mere  spreading  of  a  local  contraction  from  the  point  stimulated. 
But  is  this  view  adequate  to  explain  the  facts?     In  the  protozoa  we 


BEHAVIOR   OF   CCELENTERATA  201 

have  found  that  such  local  action  is  as  a  rule  not  adequate;  that  the 
organism  tests  the  environment;  and  the  behavior  at  a  given  moment 
depends  on  the  success  or  failure  of  a  previous  trial.  Is  there  anything 
of  this  kind  in  the  medusa,  or  does  Loeb's  simple  explanation  exhaust 
the  matter? 

This  question  is  clearly  answered  by  the  experiments  of  Romanes. 
He  found  that  if  a  cut  is  made  parallel  to  the  margin,  as  at  x,  Fig.  125, 
and  a  point  lying  below  this  cut  is  stimulated,  the  manubrium  is  no 
longer  able  to  locate  precisely  the  stimulated  point.  It  bends,  but  no 
longer  directly  to  the  point  stimulated.  This,  according  to  Loeb,  is 
exactly  what  we  should  expect.  The  cut  interrupts  certain  of  the  lines 
of  tension,  so  that  they  no  longer  pull  the  manubrium  to  the  precise  spot. 
His  explanation,  he  holds,  "  also  shows  why  an  incision  parallel  to  the 
margin  of  the  umbrella  makes  an  exact  localization  impossible  and  only 
allows  uncertain  movements  toward  the  stimulated  quadrant"  (1900, 
p.  32).  It  is  easy  to  see  that  the  manubrium,  on  Loeb's  theory  of  de- 
composition of  the  lines  of  tension,  would  be  pulled  over  in  the  general 
direction  of  the  stimulated  spot,  but  might  not  strike  it  exactly. 

Is  this  what  happens?  Let  us  examine  the  facts  as  set  forth  in 
Romanes'  own  words:  "Although  in  the  experiment  just  described 
the  manubrium  is  no  longer  able  to  localize  the  seat  of  stimulation  in 
the  bell,  it  nevertheless  continues  able  to  perceive,  so  to  speak,  that 
stimulation  is  being  applied  in  the  bell  somewhere,  for  every  time  any 
portion  of  tissue  below  the  cut  a  is  irritated,  the  manubrium  actively 
dodges  about  from  one  part  of  the  bell  to  another,  applying  its  extremity 
now  to  this  place  and  now  to  that  one,  as  if  seeking  in  vain  for  the  of- 
fending body.  If  the  stimulation  is  persistent,  the  manubrium  will 
every  now  and  then  pause  for  a  few  seconds,  as  if  trying  to  decide  from 
which  direction  the  stimulus  is  proceeding,  and  will  then  suddenly 
move  over  and  apply  its  extremity,  perhaps  to  the  point  that  is  opposite 
the  one  which  it  is  endeavoring  to  find.  It  will  then  suddenly  leave 
this  point  and  try  another,  and  so  on,  as  long  as  the  stimulation  is  con- 
tinued" (Romanes,  1885,  p.  112-113). 

From  Romanes'  description  it  is  evident  that  the  manubrium  under 
these  circumstances  may  not  even  move  in  the  general  direction  of  the 
point  stimulated ;  he  says  expressly  that  it  may  move  toward  the  oppo- 
site point,  or  toward  any  other  point.  At  times,  he  says,  a  manubrium 
moves  from  point  to  point,  "without  being  able  in  the  least  degree  to 
localize  the  seat  of  irritation."  The  considerations  adduced  by  Loeb 
do  not  explain  these  facts;  and  his  theory  is  quite  inadequate  to  account 
for  the  behavior.  Contraction  occurs,  not  merely  as  a  direct  spreading 
from  the  point   stimulated,  but   now  in  one  place,   now  in   another, 


202  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

including  even  a  region  directly  opposite  that  stimulated.  The  manu- 
brium, having  reacted  once,  does  not  cease,  but  in  some  way  recognizes 
its  failure  and  tries  again.  In  other  words,  failure  changes  its  physio- 
logical state,  so  that  now  it  bends  in  a  new  direction.  The  whole 
account  given  by  Romanes  is  as  vivid  a  description  of  the  method  of 
reaction  by  the  production  of  varied  movements  subjecting  the  organism 
successively  to  different  conditions,  as  it  would  be  possible  to  imagine 
under  these  circumstances. 

It  would  be  most  interesting  to  determine  whether  the  animal  may 
thus  by  trial  finally  discover  the  irritated  spot,  and  later  through  repeti- 
tion come  to  bend  toward  it  directly,  as  it  did  before  the  cut  was  made. 

5.     The  Rejecting  Reaction  of  Sea  Anemones 

In  some  sea  anemones  the  presence  of  masses  of  waste  matter  on 
the  disk  leads  to  the  performance  of  activities  which  result  in  the  re- 
moval of  the  waste  matter;  this  behavior  we  may  call  the  rejecting  reac- 
tion. Such  behavior  is  well  seen  in  the  large  sea  anemone  Stoichactis 
helianthus,  found  in  the  West  Indies.  This  animal  has  a  flat  or  concave 
disk  10  to  15  cm.  in  diameter,  covered  closely  with  tentacles  about 
8  mm.  in  length.  If  a  quantity  of  dead  plankton,  or  a  mass  of  sand, 
or  other  waste  matter,  is  placed  on  the  disk,  the  animal  sets  in  opera- 
tion measures  which  remove  it.  Food  placed  on  the  disk  of  a  speci- 
men that  is  not  hungry  produces  the  same  result.  The  behavior  under 
such  circumstances  is  complex,  and  the  removal  of  the  waste  matter 
may  be  accomplished  in  more  than  one  way. 

The  tentacles  of  that  region  of  the  disk  bearing  the  waste  body  col- 
lapse, becoming  thin  and  slender  and  lying  flat  against  the  disk.  The 
disk  surface  in  this  region  begins  to  stretch,  separating  the  collapsed 
tentacles  widely.  As  a  result  the  waste  mass  is  left  on  a  smooth,  exposed 
surface,  the  tentacles  here  having  practically  disappeared,  while  else- 
where they  form  a  close  investment.  Thus  the  waste  is  left  fully  ex- 
posed to  the  action  of  the  waves  or  currents,  and  the  slightest  disturbance 
in  the  water  washes  it  off.  Under  natural  conditions  this  must  result 
in  an  immediate  removal  of  the  mass  of  debris.  If  this  does  not  occur 
at  once,  often  the  region  on  which  the  debris  is  resting  begins  to  swell, 
becoming  a  strongly  convex,  smooth  elevation,  thus  rendering  the  wash- 
ing away  of  the  mass  still  easier. 

But  if  the  debris  is  not  removed  by  the  reaction  just  described,  then 
new  activities  set  in.  If  the  waste  body  is  near  one  edge  of  the  disk, 
this  edge  usually  begins  to  sink,  while  at  the  same  time  the  tentacles  be- 
tween the  edge  and  the  waste  mass  collapse  and  practically  efface  them- 


BEHAVIOR   OF   CCELENTERATA  203 

selves.  Thus  the  mass  slides  downward  off  the  disk.  If  this  does  not 
occur  at  once,  after  a  time  the  region  lying  behind  the  mass  begins  to 
swell ;  it  often  forms  in  this  way  a  high,  rounded  elevation.  The  waste 
mass  is  now  on  a  steep  slope,  and  is  bound  soon  to  slide  over  the  edge. 
Sometimes  by  a  continuation  of  these  processes  the  entire  disk  comes 
to  take  a  strongly  inclined  position,  with  the  side  bearing  the  debris 
below.  Often  one  portion  of  the  edge  after  another  is  lowered  succes- 
sively till  all  of  the  waste  matter  is  removed  and  the  disk  is  thoroughly 
cleaned.  The  disk  then  resumes  its  horizontal  position,  with  nearly 
flat  or  slightly  concave  surface. 

Sometimes  the  edge  bearing  the  debris  cannot  be  lowered,  owing  to 
the  fact  that  it  is  almost  against  an  elevation  in  the  irregular  rock  to 
which  the  anemone  is  attached.  In  this  case  (after  perhaps  an  attempt 
to  bend  this  edge  downward)  the  part  between  this  edge  and  the  debris 
swells  and  rises,  rolling  the  mass  toward  the  centre,  while  at  the  same 
time  the  region  beyond  the  debris  sinks  down.  In  this  way  the  waste 
matter  is  rolled  across  the  disk  to  the  opposite  side,  and  dropped  over 
the  edge.  The  process  is  slow,  often  requiring  fifteen  minutes  to  half 
an  hour. 

This  whole  reaction  is  characterized  by  great  flexibility  and  vari- 
ability. The  debris  sets  in  operation  certain  activities;  if  these  do  not 
put  an  end  to  the  stimulation,  other  activities  are  induced,  till  one  is 
successful.  This  is  an  excellent  illustration  of  the  general  characteris- 
tics of  behavior  in  the  lower  organisms. 

6.    Locomotor  Reactions  in  Hydra  and  Sea  Anemones 

After  contracting  in  response  to  stimulation,  if  the  stimulus  still 
continues,  Hydra  and  the  sea  anemones  usually  set  in  operation  other 
activities,  having  a  more  radical  effect  in  separating  the  animal  from 
the  source  of  stimulation.  We  have  examined  certain  cases  of  this 
character  in  the  foregoing  section  on  the  rejecting  reaction.  We  shall 
here  consider  such  reactions  as  tend  to  remove  the  animal,  or  cause  it 
to  take  a  new  position. 

Hydra.  —  After  contracting  in  response  to  stimulation,  Hydra  usu- 
ally bends  over  into  a  new  position  and  soon  extends  again  in  a  new 
direction,  just  as  happens  in  its  spontaneous  contractions  (Fig.  114). 
This  may  be  repeated  many  times,  the  animal  occupying  successively 
many  different  positions. 

In  bending  thus  into  a  new  position  in  response  to  a  one-sided  stim- 
ulus, does  Hydra  bend  directly  away  from  the  source  of  stimulation? 
Wagner  (1905)  and  Mast  (1903)  have  answered  this  question  experi- 


204  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

mentally.  Wagner  tried  stimulating  one  side  of  the  body  mechanically, 
while  Mast  raised  or  lowered  the  temperature  of  one  side.  Both  authors 
agree  as  to  the  following  results:  The  direction  of  extension  after  con- 
traction bears  no  definite  relation  to  the  side  from  which  the  stimulus 
came;  the  animal  is  just  as  likely  to  extend  toward  the  source  of  stimu- 
lation as  in  any  other  direction.  In  other  words,  when  stimulated, 
Hydra  merely  changes  its  position,  without  special  relation  to  the  locali- 
zation of  the  stimulating  agent.  The  direction  of  bending  and  exten- 
sion is  determined  by  internal  factors.  If  the  stimulus  is  repeated,  con- 
traction occurs  again,  and  the  animal  extends  in  still  another  direction. 
The  analogy  of  these  relations  with  those  shown  by  the  infusoria  is  evi- 
dent; the  latter  when  stimulated  usually  merely  change  the  direction 
of  movement,  without  regard  to  the  direction  from  which  the  stimulus 
came.  In  the  infusoria  the  internal  factors  (structural  in  character) 
which  determine  the  direction  have  been  determined;  this  has  not  yet 
been  done  for  Hydra. 

But  repeated  or  strong  continued  contraction,  with  extension  in  a 
new  direction,  is  not  the  final  recourse  of  Hydra  under  strong  stimula- 
tion. If  the  stimulation  continues,  the  animal  finally  bends  over,  places 
its  head  against  the  surface  to  which  it  is  attached,  releases  its  foot,  and 
moves  away  from  the  spot  where  it  has  been  subjected  to  such  objec- 
tionable experiences.  The  locomotion  is  usually  of  the  sort  illustrated 
in  Fig.  117.  This  reaction  has  been  observed  by  Wagner  (1905)  under 
mechanical  stimulation,  by  Mast  (1903)  under  stimulation  by  heat,  and 
by  the  present  author  under  stimulation  by  chemicals.  In  all  cases  it 
was  found  that  the  direction  toward  which  the  animal  moves  bears  no 
definite  relation  to  the  direction  from  which  the  stimulus  comes.  Wag- 
ner stimulated  one  side  repeatedly  by  striking  it  with  a  rod,  and  found 
that  the  animal  was  as  likely  to  move  toward  that  side  as  in  any  other 
direction.  The  experiments  of  Mast  are  particularly  interesting  in  this 
connection.  Mast  placed  a  considerable  number  of  Hydras  in  a  fiat- 
bottomed  trough,  and  heated  one  end.  At  about  31  degrees  C.  the 
animals  began  to  release  their  foothold  and  move  about  from  place 
to  place.  But  they  were  as  likely  to  move  toward  the  heated  end  as 
away  from  it.  The  results  of  a  series  of  such  experiments  are  shown 
in  Fig.  127.  In  this  figure  are  represented  not  only  the  movements  of 
locomotion,  but  also  the  different  directions  in  which  the  animal  ex- 
tended after  contracting.  The  diagram  shows  clearly  that  both  sets  of 
movements  are  quite  without  definite  relation  to  the  direction  from  which 
the  heat  comes;  their  direction  evidently  depends  on  internal  factors. 
When  it  experiences  the  high  temperature,  the  animal  merely  changes 
its  position,  in  a  way  determined  by  its  structure  or  other  internal  fac- 


BEHAVIOR   OF   CCELENTERATA 


205 


tors.  If  the  high  temperature  still  continues,  it  changes  position  again, 
and  thus  continues  till  the  high  temperature  ceases  or  the  animal  dies. 
The  behavior  resembles  essentially  that  of  infusoria  under  similar  con- 
ditions. The  reaction  is  very  ineffective  under  the  conditions  shown  in 
Fig.  127,  owing  to  the 


slowness  of  the  move- 
ments of  Hydra.  Most 
of  the  animals  in  the 
heated  region  finally  die. 
But  if  the  animals  moved 
rapidly  and  far  at  each 
change  of  position,  then 
those  that  moved  away 
from  the  heated  side 
would  escape,  and  those 
that  moved  in  the 
wrong  direction  the  first 
time  would,  after  one 
or  two  changes  of  di- 
rection, likewise  get  out 
of  the  heated  region. 
The  reaction  would  be 
of  precisely  the  same 
character  as  that  of  the 


8 


28' 


23' 


GL 


\ 


t 


-g 


infusoria.            But        the  Fig.    127.  —  Diagram  of  the   movements   of  a  number  of 

action   SVStem  of  HvdrT  Hydras  when  the  trough  containing  them  was  heated  at  the  end 

•*                          ^  to  the  left.     Each  of  the  small  diagrams  represents  the  move- 

is        evidently       adapted  ments  of  a  single  Hydra.     The  figures  i,  2,  3,  etc.,  show  the 

onlv      for       mpptino-  successive  different   directions    in  which   the   Hydra   extended 

*                     .                    &  while  remaining  attached.      The  cross  (  X  )  between  two  num- 

changed  Conditions  Over  bers   indicates    that  here  the  animal  released  its  foothold  and 

a  VPrv  limited  arpa   surh  moved  m  the  direction  shown  to  a  new  point  of  attachment. 

^                              '  After  Mast  (1903). 

as  may  be  escaped  by  a 

slight,  slow  movement.  When  the  changed  conditions  cover  too  large 
an  area,  the  Hydra  can  only  "try"  its  usual  reaction;  if  this  fails,  it 
must  die. 

A  decrease  of  temperature  does  not  cause  Hydra  to  change  position. 
As  the  temperature  becomes  lower,  the  animal  merely  becomes  more 
sluggish,  contracting  more  slowly  and  at  longer  intervals,  till  finally, 
near  the  freezing  point,  movement  almost  ceases  (Mast). 

As  we  have  seen  on  page  194,  an  internal  condition  —  hunger  — 
may  induce  the  same  locomotor  reactions  as  are  produced  by  continued 
external  stimulation.  This  is  a  matter  which  we  shall  take  up  again  in 
the  account  of  food  reactions. 


206  BEHAVIOR    OF   THE   LOWER   ORGANISMS 

Sea  Anemones. — In  some  sea  anemones,  as  in  Hydra,  repeated 
strong  stimulation  causes  the  animal  first  to  contract,  then  to  bend  into 
new  positions,  and  finally  to  move  away.  Each  of  these  reactions  may 
be  repeated  several  times  before  the  succeeding  one  occurs.  There  are 
certain  features  of  this  behavior  that  are  of  much  interest,  since  they  lead 
to  results  analogous  to  habit  formation  in  higher  animals.  The  facts 
have  been  most  carefully  studied  in  Aiptasia  annulate. 

Aiptasia  is  a  rather  slender,  somewhat  elongated  actinian  living  in 
crevices  beneath  and  between  stones.  If  stimulated  by  touching  the 
disk  or  tentacles  with  a  rod,  it  contracts  strongly.  It  then  extends  in 
the  same  direction  as  before.  When  it  is  fully  extended  we  repeat  the 
stimulus.  The  animal  responds  in  the  same  way  as  at  first.  This  con- 
tinues usually  for  about  ten  or  fifteen  stimulations,  the  animal  extending 
each  time  in  the  same  direction  as  at  first.  But  at  length,  when  stimu- 
lated anew,  the  polyp  contracts,  bends  over  to  one  side,  and  extends  in 
a  new  direction.  As  the  stimuli  are  continued,  the  animal  repeats  for  a 
number  of  times  the  contraction  and  extension  in  the  new  direction, 
then  finally  turns  and  tries  a  still  different  position. 

This  change  of  position  may  be  repeated  many  times.  But  in  the 
course  of  time  the  reaction  becomes  changed  in  a  still  different  manner. 
The  anemone  releases  its  foothold  and  moves  to  a  new  region.  This 
same  reaction  is  produced  in  Cerianthus,  as  we  have  seen,  by  hunger. 

Aiptasia  frequently  extends  in  most  awkward  turns,  the  body  taking 
and  retaining  an  irregular  and  even  crooked  form.  This  is  evidently 
due  to  its  life  in  irregular  crevices  and  crannies.  In  order  that  its  disk 
may  protrude  into  the  open  water,  it  is  compelled  to  extend  in  the  irreg- 
ular ways  mentioned,  and  to  retain  the  crooked  shapes  thus  produced. 
"When  removed  from  its  natural  habitat,  it  still  retains  these  irregulari- 
ties of  form  and  action,  so  that  a  collection  of  Aiptasias  shows  all  sorts 
of  right-angled  and  zigzag  shapes.  It  would  appear  that  these  irregu- 
larities must  have  arisen  as  a  result  of  the  way  in  which  the  animal 
extends  in  its  natural  surroundings.  From  this  it  would  appear  that  a 
method  of  extension  frequently  repeated  must  in  the  course  of  time 
become  stereotyped,  forming  what  we  are  accustomed  to  call  in  higher 
animals  a  habit. 

If  this  is  the  case,  then  it  should  be  possible  to  produce  new  stereo- 
typed reaction  forms,  by  so  arranging  the  conditions  that  the  animal 
shall  be  compelled  to  extend  always  in  a  certain  way  (differing  from 
its  former  way),  and  to  retain  the  form  thus  induced.  In  some  speci- 
mens this  result  is  obtained  with  the  greatest  ease,  and  in  a  very  simple 
manner.  Thus,  in  a  certain  case,  an  individual  attached  to  a  plane 
horizontal  glass  surface  was  bent  in  extension  far  over  to  the  left.   Stimu- 


BEHAVIOR   OF   CCELENTERATA  207 

lating  it  repeatedly,  it  contracted  at  each  stimulation,  then  bent,  in 
extending,  again  to  the  left.  But  after  some  fifteen  stimulations  it 
turned  away,  and  bent  over  to  the  right.  Now  when  stimulated  it  con- 
tracted as  before,  then  bent  regularly,  in  extending,  over  to  the  right. 
It  seemed  to  have  acquired  a  new  method  of  behaving,  bending  to 
the  right  instead  of  to  the  left. 

Close  examination  showed  that  the  cause  of  this  phenomenon  is  as 
follows:  When  it  contracts  in  response  to  stimulation,  it  does  not  re- 
gain a  completely  symmetrical  structure,  but  remains  a  little  more  con- 
tracted on  the  side  that  is  concave  in  extension.  In  extending  anew, 
this  side  still  remains  a  little  more  contracted  than  the  opposite  one,  so 
the  animal  takes  a  curved  form,  concave  toward  the  same  side  as  in  its 
previous  extension.  In  other  words,  the  structure  conditioning  the 
curved  form  is  not  completely  lost  even  when  the  animal  contracts,  and 
it  becomes  evident  again  on  a  new  extension. 

Thus  in  Aiptasia  the  formation  of  a  stereotyped  method  of  action 
depends  upon  very  simple  conditions.  Yet  there  can  hardly  be  a  doubt 
that  the  permanent  individual  peculiarities  of  form  and  action  found 
under  natural  conditions,  as  mentioned  above,  have  risen  in  exactly 
this  way.  It  thus  plays  the  part  taken  by  what  is  called  habit  formation 
in  higher  animals. 

The  facts  set  forth  in  the  present  section  show  clearly  that  the  cce- 
lenterates  do  not  always  react  in  the  same  way  to  the  same  external 
stimulus.  Internal  conditions  of  the  organism,  as  determined  by  past 
stimuli  received,  past  reactions  given,  and  various  other  factors,  are  of 
equal  importance  with  external  conditions  in  determining  behavior. 
We  shall  see  many  further  illustrations  of  this  fact  in  the  reactions 
toward  food. 

7.    Acclimatization  to  Stimuli 

Besides  the  changes  in  behavior  under  constant  stimuli  that  we  have 
described  in  the  last  section,  there  are  certain  others  which  may  perhaps 
be  classed  as  acclimatization  to  stimulation.  In  sea  anemones  a  light 
stimulus  that  is  not  injurious  may  cause  at  first  a  marked  reaction,  then 
on  repetition  produce  no  reaction  at  all,  or  a  very  slight  one.  Thus,  a 
drop  of  water  is  allowed  to  fall  from  a  height  of  30  cm.  on  the 
surface  of  the  water  just  above  the  outspread  disk  of  Aiptasia  annulata. 
The  animal  at  once  contracts  completely.  After  the  animal  has 
expanded,  another  drop  is  allowed  to  fall  in  the  same  way.  As  a  rule, 
there  is  no  response  to  this  or  to  succeeding  drops.  Sometimes  there 
is  a  reaction  to  the  first  two  or  even  three  drops,  but  usually  reaction 
ceases  after  the  first  one. 


208 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


Sometimes  a  slight  reaction  of  a  different  character  supervenes  after 
the  stimulus  has  been  repeated  many  times.  The  animal  begins  to 
shrink  slowly  away  from  the  region  where  the  drops  are  falling,  so  that 
in  the  course  of  time  the  disk  has  been  withdrawn  much  farther  be- 
low the  surface,  though  no  decided  reaction  has  occurred  to  any  one 
stimulus. 

8.    Reactions  to  Certain  Classes  of  Stimuli 

In  the  foregoing  sections  we  have  taken  up  reactions  to  mechanical 
stimuli,  heat  and  cold,  and  chemicals;  we  shall  have  occasion  to  con- 
sider some  of  these  further  in  the  account  of  food  reactions.  There  are 
certain  other  classes  of  external  stimuli  which  may  play  a  part  in  deter- 
mining behavior  in  these  animals ;  these  we  will  take  up  separately. 


A.   Reactions  to  Electricity 

Induction  shocks  have  been  much  employed  in  experimental  work 
on  contraction  in  ccelenterates.     The  results  of  such  stimulation  do  not 


SO- 


Fig.  128.  —  Reaction  of  an  attached  Hydra  to  a  constant  electric  current  of  moderate  inten- 
sity.    1-5,  successive  stages  in  the  reaction.     After  Pearl  (1901). 

differ  greatly  from  those  produced  by  other  forms  of  stimulation  (me- 
chanical, etc.),  local  or  general  contractions  occurring  in  dependence 
on  the  strength  of  the  current.  These  may  be  followed  by  locomotor 
movements. 

The  effects  of  the  constant  electric  current  are  more  peculiar  and  of 
greater  interest.  They  have  been  studied  in  Hydra  by  Pearl  (1901); 
in  the  medusa  Polyorchis  penicillata  by  Bancroft  (1904). 

Hydra.  —  In  Hydra  the  constant  current  causes  local  bendings  of 
the  body  similar  to  those  produced  by  sharply  localized  chemical  and 
thermal  stimuli.  If  a  weak  current  is  passed  through  the  water  trans- 
versely to  the  Hydra,  the  animal  contracts  on  the  anode  side,  at  a  point 
a  little  above  the  foot,  thus  bending  the  body  (Fig.  128).  At  the  same 
time  or  a  little  before,  the  tentacles  which  were  in  line  with  the  current 
contract  (Fig.   128,  a).     Sometimes,  further,  there  is  a  contraction  on 


BEHAVIOR  OF   CCELENTERATA 


209 


the  anode  side  just  below  the  base  of  the  tentacles.  As  a  result  of  the 
contraction  on  the  anode  side,  the  Hydra  bends  toward  the  anode.  As 
soon  as  it  comes  into  a  position  wi^h  the  anterior  end  directed  toward 
the  anode,  the  entire  body  contracts,  since  a  Hydra  in  this  position  is 
stimulated  more  than  in  any  other  (Fig.  128,  5).  In  a  stronger  current 
the  complete  contraction  takes  place  first,  then  the  animal  slowly  bends 
over  toward  the  anode.  If,  as  sometimes  happens,  the  foot  is  free  while 
the  head  is  attached,  the  bending  takes  place  as  usual  on  the  anode  side. 


Fig.  129.  — Successive  stages  in  the  reaction  of  a  Hydra  to  the  electric  current  when  the 
foot  is  unattached.     The  foot  becomes  directed  toward  the  anode.     After  Pearl  (1901). 

The  result  is  necessarily  that  the  foot  becomes  directed  toward  the  anode, 
so  that  in  this  case  the  orientation  of  the  animal  is  the  reverse  of  that 
found  in  the  specimens  attached  by  the  foot  (Fig.  129).  This  result 
shows  clearly  that  the  orientation  to  the  electric  current  is  due  to  the 
direct  local  contractions  caused  by  the  current  on  the  anode  side,  and 
is  not  due  to  an  attempt  on  the  part  of  the  animal  by  anything  like  a 
process  of  trial  to  come  into  a  certain  definite  position. 

In  a  Hydra  placed  transversely  to  the  current,  the  tentacles  con- 
tract in  a  peculiar  way.  A  weak  current  causes  only  the  tentacles  which 
are  in  line  with  the  current  to  contract,  and  of  these,  that  extending 
toward  the  cathode  contracts  more  quickly  and  more  completely  than 


-   + 


B 


Fig.  130.  —  Fffects  of  the  constant  electric  current  on  pieces  of  Polyorchis.  After  Bancroft 
(1Q04).  A,  meridional  strip  passing  through  the  manubrium.  B,  similar  strip  stretched  out 
in  line  with  the  current.     C,  isolated  tentacles. 

that  directed  toward  the  anode  (Fig.  128,  a).  If  the  Hydra  is  lying 
parallel  with  the  current,  the  body  contracts  much  more  readily  when 
the  anterior  end  is  directed  toward  the  anode  than  when  it  is  directed 
toward  the  cathode.  In  either  of  these  positions  the  tentacles  usually 
remain  extended,  and  somewhat  inclined  toward  the  cathode  (Figs.  128 
and  129).     But  if  a  very  strong  current  is  used,  both  body  and  ten- 


210  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

tacles  contract  strongly.  Pieces  of  the  animal  react  in  essentially  the 
same  way  as  the  entire  organism,  and  young  buds  (with  tentacles) 
react  in  the  same  way  as  adults,  but  are  more  sensitive  to  the  current 
(Pearl,  190 1). 

Medusa.  —  If  strips  of  various  shapes  are  cut  from  the  medusa 
Polyorchis,  and  subjected  to  the  action  of  the  constant  current,  the 
tentacles  and  manubrium  bend  toward  the  cathode  (Fig.  130,  a,  b). 
This  takes  place  even  with  isolated  tentacles  (Fig.  130,  c).  If  the 
current  is  long  continued,  such  isolated  tentacles  partially  relax,  then 
contract  again.  This  is  repeated,  so  that  an  irregular  rhythmic  con- 
traction is  produced  by  the  constant  current. 

B.   Reactions  to  Gravity 

The  position  of  the  body  and  the  direction  of  locomotion  are  partly 
determined  in  some  of  the  Ccelenterata  by  gravity.  There  is  great 
diversity  among  different  members  of  the  group  in  this  respect.  In 
some,  gravity  is  an  almost  constant  determining  factor  in  the  behavior. 
In  others  it  plays  only  an  incidental  part,  affecting  the  behavior  under 
certain  circumstances,  while  in  still  other  cases  it  seems  to  have  no  effect 
on  the  movements  whatsoever. 

We  have  already  seen  that  the  position  taken  by  Cerianthus  is  partly 
determined  by  gravity.  The  sea  anemone  Sagartia,  according  to  Torrey 
(1904),  usually  moves  upward  when  this  is  possible,  and  at  the  same 
time  it  tends  to  keep  its  body  in  line  with  gravity,  with  the  disk  above. 
If  while  moving  on  the  floor  of  the  aquarium  it  reaches  the  perpendicu- 
lar side,  it  at  once  begins  to  ascend.  Since  Sagartia  creeps  by  move- 
ments of  its  foot,  remaining  in  the  upright  position,  its  ascent  on  a 
vertical  surface  involves  bringing  the  body  into  an  oblique  position, 
in  place  of  the  usual  perpendicular  one.  Thus  its  tendency  to  creep 
upward  interferes  with  its  tendency  to  keep  its  body  in  line  with  gravity, 
and  the  former  prevails.  Sagartia  may  also  creep  on  the  under  side 
of  the  surface  film,  with  head  down,  so  that  it  is  by  no  means  a  rigid 
requirement  that  the  head  shall  be  above.  Doubtless  many  other  sea 
anemones  will  show  a  tendency  to  keep  the  body  in  a  certain  position 
with  reference  to  gravity. 

In  the  hydroid  Corymorpha,  according  to  Torrey  (1904  a),  there  is 
a  decided  tendency  to  take  a  position  with  the  head  (or  oral  end)  upward. 
When  placed  in  an  inverted  or  oblique  or  horizontal  position,  Cory- 
morpha rights  itself  by  a  bending  of  the  body,  which  is  due,  according 
to  Torrey,  not  to  muscular  contraction,  as  in  the  sea  anemones,  but  to 
a  change  in  the  turgidity  of  the  large  axial  entoderm  cells.     Those  on 


BEHAVIOR   OF   CCELENTERATA  21 1 

the  lower  side  become  more  turgid,  increasing  in  volume  and  thus  bend- 
ing the  stem  directly  upward.  Either  the  entire  animal  or  a  piece  of 
the  stem,  without  head  or  foot,  reacts  in  this  manner.  Thus  the  reaction 
is  in  this  animal  comparable  to  the  reaction  to  gravity  in  a  plant. 

But  in  many  species  of  fixed  ccelenterates  gravity  clearly  has  little 
or  nothing  to  do  with  the  usual  position.  Metridium,  Aiptasia,  Stoi- 
chactis  kelianthus,  Condylactis  passiflora,  and  many  others  are  found 
occupying  all  sorts  of  positions  with  reference  to  gravity,  and  the  same 
is  true  of  Hydra  and  various  hydroids. 

In  some  medusae  the  movement  is  partly  guided  by  gravity.  Go- 
nionemus,  as  we  have  seen,  swims  in  its  "fishing"  movements  upward 
to  the  surface.  Yerkes  (1903)  found  that  this  occurs  in  the  same  way 
when  the  light  comes  from  below,  so  that  the  guiding  factor  is  apparently 
gravity.  This  reaction  to  gravity  is  of  course  not  constant;  it  occurs 
only  at  intervals  and  under  certain  circumstances. 

Careful  examination  will  probably  show  that  gravity  plays  a  part  in 
certain  episodes  of  the  behavior  of  most  of  these  animals,  even  though 
it  may  not  affect  their  usual  position  or  direction  of  motion.  Thus, 
gravity  plays  a  part  in  the  "rejecting  reaction"  of  the  actinian  Stoi- 
chactis,  described  in  Section  5  of  the  present  chapter.  The  situa- 
tion "  waste-matter-on-the-disk-not-removed-by-the-first-reaction  "  is 
responded  to  by  taking  such  a  position  with  reference  to  gravity  as  re- 
sults in  removing  the  waste ;  then  the  reaction  to  gravity  ceases.  Simi- 
lar transitory  reactions  to  gravity,  seeming  to  serve  definite  ends,  are 
found  in  many  other  animals.  Thus,  in  the  hermit  crab,  according  to 
Bohn  (1903),  we  have  such  a  case.  While  investigating  a  shell  which 
it  may  adopt  as  a  home  if  fitting,  this  animal  takes  a  certain  position 
with  reference  to  gravity;  namely,  with  body  on  the  steepest  slope  of 
the  shell,  and  head  downward.  It  then  turns  the  shell  over  (the  posi- 
tion mentioned  being  the  most  favorable  one  for  this  action),  and  ceases 
to  react  with  reference  to  gravity.  Other  cases  of  the  same  sort  will  be 
described  for  the  flatworm  Convoluta  (Chapter  XII).  Gravity  has,  of 
course,  many  diverse  effects  on  the  substance  of  organisms,  and  in  al- 
most no  case  has  its  precise  action  in  directing  movements  been  deter- 
mined. When  an  animal  is  inverted,  this  may  cause  a  redistribution 
of  the  constituents  of  the  body  or  of  the  separate  cells.  Such  a  redis- 
tribution would  probably  interfere  with  the  usual  physiological  pro- 
cesses, and  might  therefore  act  as  a  stimulus  to  a  change  of  position. 
Again,  in  freely  moving  organisms,  gravity  causes  differences  in  the 
ease  of  movement  in  different  directions,  and  such  differences  may 
well  determine  the  direction  of  motion.  Again,  a  change  in  the  usual 
position  with  reference  to  gravity  may  induce  unusual  strains  in  various 


212  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

parts  of  the  body,  or  may  shift  the  weight  of  the  body  to  parts  unaccus- 
tomed to  bearing  it;  and  these  effects  might  serve  as  stimuli  to  cause 
the  animal  to  take  another  position.  This  possibility  will  be  vividly 
realized  by  any  one  who  undertakes  to  rest  with  a  limb  doubled  in  some 
unusual  position  beneath  him.  Again,  certain  movements  with  refer- 
ence to  gravity  may  produce  results  involving  a  change  of  the  conditions 
affecting  the  organism,  and  since  it  is  a  well-established  fact  that  the 
results  of  behavior  partly  determine  future  behavior,  this  fact  may 
determine  movements  with  reference  to  gravity.  There  seems  to  be 
no  a  priori  reason  why  each  of  the  relations  above  mentioned,  as  well 
as  various  others,  may  not  induce  reaction  in  one  organism  or  another, 
and  it  seems  not  difficult  to  find  probable  examples  of  all.  We  have 
been  assured  by  various  writers  that  the  reaction  to  gravity  must  be 
explained  in  the  same  way  in  all  cases,  but  this  is  evidently  said  rather 
in  the  capacity  of  a  seer  or  prophet,  than  in  the  capacity  of  a  man  of 
science  whose  conclusions  are  inductions  from  observation  and  experi- 
ment. 

C.    Reactions  to  Light 

Many  of  the  sea  anemones  and  medusae  do  not  react  to  light,  so  far 
as  known.  In  other  cases  a  reaction  to  light  is  very  marked.  The 
relation  of  the  behavior  to  light  is  in  certain  cases  exceedingly  complex, 
and  very  instructive,  as  showing  the  numerous  factors  on  which  behavior 
depends.  We  shall  take  up  especially  the  reactions  of  Hydra,  and  of 
the  medusa  Gonionemus. 


(i)  Reaction  to  Light  in  Hydra 

The  behavior  of  Hydra  with  relation  to  light  has  been  studied  es- 
pecially by  Wilson  (1891).  Both  the  green  and  the  brown  Hydra  are 
usually  found  at  the  lighted  side  of  the  vessel  containing  them.  If  they 
are  at  first  scattered,  they  will  in  a  day  or  two  be  found  to  have  moved 
to  the  lighted  side.  If  at  the  side  of  the  dish  next  the  window  there  are 
attached  light  and  dark  strips  of  glass,  the  Hydras  collect  in  the  light 
strips.  If  different  colored  lights  are  used,  by  placing  strips  of  glass 
of  different  colors  on  the  lighted  side  of  the  vessel,  the  Hydras  collect 
in  the  blue  light,  while  all  other  colors  (except  perhaps  green,  which 
seems  slightly  effective)  act  like  darkness.  The  animals  gather  in  the 
blue  even  in  preference  to  the  white  light,  which  of  course  contains  all 
the  blue  rays.  As  to  the  way  in  which  the  reaction  to  light  takes  place, 
the  following  facts  were  brought  out  by  Wilson.  A  change  from  light 
to  dark,  or  from  blue  or  white  light  to  one  of  the  colors  which  acts  like 


BEHAVIOR  OF  CCELENTERATA  213 

darkness,  causes  the  animal  to  become  restless  and  move  about.  The 
motion  seems  undirected,  but  as  soon  as  the  animal  comes  into  the  blue 
or  white  light,  it  becomes  less  restless,  and  remains.  The  behavior 
is  thus  far,  then,  like  the  reaction  to  heat;  the  animal  when  not  lighted 
simply  moves  about  in  various  directions,  till  one  of  its  movements 
brings  it  into  light.  Whether  the  animal  when  moving  draws  back  or 
stops  on  coming  to  the  boundary  of  the  light,  where  it  would  pass  into 
the  darkness,  as  Euglena  does,  has  not  been  determined.  But  when  the 
vessel  is  lighted  from  one  side,  the  animal  moves  toward  the  source 
of  light,  and  the  movement  is  no  longer  an  irregular  wandering,  but 
according  to  Wilson  (1891^.432)  is  fairly  direct.  This  is  like  there- 
action  of  Euglena,  and  it  seems  possible  that  in  Hydra  the  reaction  is 
produced  in  the  same  manner  as  in  that  organism.  If  this  is  true, 
there  is  a  tendency  for  the  moving  animal  to  keep  its  anterior  end  directed 
toward  the  light,  due  to  the  fact  that  when  it  turns  this  end  away,  the 
change  to  relative  obscurity  at  the  anterior  end  causes  further  move- 
ment, till  the  light  again  falls  on  the  anterior  end.  The  movements 
should  be  studied  further  to  determine  this  point.  Fixed  Hydras  do 
not  maintain  any  particular  orientation  with  reference  to  the  light  rays, 
but  change  their  position  frequently,  in  the  way  illustrated  in  Fig.  1 14. 
The  green  Hydra  moves  to  the  lighted  side  of  the  vessel  more  rapidly 
than  the  yellow  Hydra.  This  is  probably  due  to  the  generally  more 
rapid  movements  of  the  green  species. 

In  a  powerful  light  the  reaction  of  Hydra,  like  that  of  most  other 
positive  organisms,  becomes  reversed.  The  animals  collect  in  the 
shadow  of  leaves  or  on  the  bottom.  They  have  not  been  observed  to 
move  directly  away  from  the  source  of  light  (Wilson,  1891),  so  that  the 
reaction  is  probably  an  irregular  wandering  based  on  the  method  of 
trial. 

Hertel  (1904)  found  that  both  the  green  and  the  colorless  Hydra 
react  by  contraction  when  subjected  to  powerful  ultra-violet  light.  These 
rays  killed  the  colorless  Hydra  in  about  one  minute,  while  Hydra  viridis 
resisted  their  action  for  six  to  eight  minutes. 

The  gathering  of  Hydras  in  lighted  areas  and  the  movement  toward 
a  source  of  moderate  light  are  of  much  benefit  to  the  animals  in  obtain- 
ing food.  Hydra  preys  upon  small  Crustacea  and  other  minute  animals, 
and  these  gather  as  a  rule  at  the  lighted  side  of  the  vessel.  By  taking 
a  position  on  this  side,  the  Hydras  find  themselves  in  the  midst  of  a  dense 
swarm  of  organisms  and  are  able  to  capture  much  food.  When  in  such 
situations  one  frequently  finds  them  gorged  with  prey.  In  other  parts 
of  the  vessel  they  would  have  almost  no  opportunity  of  obtaining  food 
(Wilson,  1 891). 


214  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

(2)    Reactions  to  Light  in  Gonionemus 

The  relation  of  the  behavior  of  the  medusa  Gonionemus  to  light,  as 
studied  by  Yerkes  (1902  a,  1903),  is  exceedingly  complex;  it  can  by  no 
means  be  expressed  by  any  simple  formula.  In  examining  the  matter 
it  will  be  well  to  consider  first  the  relation  of  the  light  to  the  amount 
of  activity  shown  by  the  animal;  then  the  nature  of  the  activities  in 
constant  lights  of  various  intensities;  then  the  effects  of  changes  of 
illumination. 

In  ordinary  daylight,  Gonionemus  continues  its  usual  activities, 
swimming  about  by  rhythmical  contractions,  and  pursuing  its  usual 
occupation  of  "fishing"  (p.  192).  It  is  not  clear  that  the  direction  of 
its  movements  has  any  relation  to  the  direction  of  the  rays  of  light,  so 
long  as  all  conditions  remain  uniform.  If  the  light  comes  from  below 
instead  of  above,  Yerkes  (1903)  found  that  Gonionemus  continues  to 
swim  to  the  top  and  float  to  the  bottom,  as  before. 

If  the  light  is  cut  off,  the  medusa  usually  comes  to  rest  after  one  to 
five  minutes.  By  covering  the  vessel  containing  them,  it  is  thus  possible 
to  bring  the  animals  to  rest  for  experimental  purposes.  In  continued 
darkness  the  animal  is  much  less  active  than  in  the  light. 

In  strong  sunlight  the  animal  becomes  very  active.  At  first  it  swims 
toward  the  source  of  light,  thus  rising  under  natural  conditions  to  the 
surface  of  the  water.  Later  its  reaction  changes ;  it  stops  coming  to  the 
surface,  begins  to  avoid  the  light,  and  swims  toward  the  bottom.  It 
may  now  persistently  strike  against  the  bottom  in  its  efforts  to  swim 
away  from  the  source  of  light.  Sometimes  in  a  strong  light  it  places 
the  more  sensitive  subumbrellar  surface  against  the  bottom  and  comes 
to  rest.  At  times  its  activities  become,  under  the  action  of  direct  sun- 
light, uncoordinated;  it  moves  upward  in  its  contraction,  downward 
in  its  expansion. 

In  a  moderate  light  coming  from  one  side  the  behavior  of  Gonio- 
nemus is  at  times  very  peculiar.  When  the  conditions  are  quite  uni- 
form, as  we  have  seen,  its  movements  often  show  no  relation  to  the  direc- 
tion of  such  a  light.  But  when  the  light  first  begins  to  act,  as  when  a 
jar  containing  medusas  is  placed  near  a  window,  they  at  first  swim 
toward  the  source  of  light.  The  medusas  thus  gather  at  the  lighted  side 
of  the  vessel.  But  after  a  time,  if  undisturbed,  they  cease  to  react  to 
light,  and  may  scatter  throughout  the  vessel.  If  there  are  regions  of 
light  and  shade,  the  animals  now  usually  gather  in  the  shaded  region. 
But  if  they  are  again  disturbed  in  some  way,  as  by  stirring  up  the  water, 
they  swim  toward  the  light  again,  —  later  scattering  as  before,  when 
the  conditions  become  uniform. 


BEHAVIOR   OF   CCELENTERATA  215 

Thus  the  reaction  of  the  animal  depends  on  its  physiological  state; 
when  excited  it  moves  toward  the  light,  otherwise  it  is  indifferent  or 
gathers  in  the  shade.  In  the  flatworms  we  find  a  parallel  condition  of 
affairs,  but  with  the  relations  reversed.  It  is  not  unlikely  that  the 
tendency  of  the  medusa  to  go  toward  the  light  when  disturbed  is  related 
to  its  usual  method  of  life,  and  has  a  functional  value.  The  animal 
when  at  rest  is  commonly  attached  to  the  vegetation  of  the  bottom. 
When  disturbed  by  a  large  animal  foraging  among  the  plants,  it  would 
move  toward  the  light,  hence  out  into  the  free  water  and  upward,  thus 
escaping  the  enemy. 

Thus  far  we  have  considered  the  behavior  under  light  of  constant 
intensity.  Let  us  now  see  the  effects  of  sudden  changes  in  intensity 
of  illumination.  Here  we  find  again  that  the  effect  of  a  given  change 
depends  on  the  state  of  the  animal.  If  the  medusa  is  at  rest  on  the 
bottom,  a  sudden  marked  increase  in  the  intensity  of  the  light  usually 
causes  a  sudden  contraction  of  the  bell.  As  a  result  the  animal,  of 
course,  swims  away  from  its  first  position.  Sometimes,  however,  an 
increase  of  light  merely  causes  an  animal  that  is  at  rest  with  the  sensitive 
concave  surface  up  to  turn  over,  so  as  to  bring  the  sensitive  surface 
against  the  bottom,  where  it  is  little  affected  by  the  light.  In  a  case 
described  by  Yerkes,  increase  of  light  caused  regularly  this  turn  with 
bell  up,  while  decrease  caused  a  return  to  the  "bell  down"  position. 

A  decrease  of  light  usually  has  no  effect  on  a  resting  Gonionemus. 
But  sometimes  it  causes  contraction,  so  that  the  medusa  swims  away. 
In  such  specimens  an  increase  of  light  usually  causes  no  reaction.  Some- 
times, however,  a  given  specimen  reacts  both  to  increase  and  decrease 
of  illumination. 

Thus  the  reaction  of  a  resting  medusa  to  a  change  of  illumination  is 
variable,  depending  on  the  individual.  Doubtless  in  a  given  individ- 
ual it  varies  with  the  physiological  state  and  past  history  of  the  animal. 

In  the  swimming  Gonionemus,  usually  both  an  increase  and  a  de- 
crease of  light  cause  the  animal  to  expand,  cease  swimming,  and  sink  to 
the  bottom.     Here  it  usually  remains  for  a  time,  then  resumes  activity. 

If  a  vessel  containing  a  number  of  the  medusae  is  divided  by  a  line 
x-x  into  two  regions,  one  brightly  illuminated,  the  other  shaded,  the 
animals  usually  behave  as  follows:  A  specimen  swimming  about  in 
the  light  region  crosses  in  its  course  the  line  x-x,  passing  into  the  shade. 
It  at  once  ceases  swimming  and  sinks  to  the  bottom.  Here  it  remains 
for  a  short  time,  then  continues  to  swim  about  in  the  shaded  region. 

If  a  specimen  swimming  in  the  shaded  region  crosses  the  line  x-x 
into  the  light,  it  likewise  sinks  to  the  bottom  and  remains  quiet  for  a 
time.     Now,  upon  resuming  activity,  it  swims  in  such  a  way  as  to  pass 


216  BEHAVIOR   OF    THE   LOWER   ORGANISMS 

back  into  the  shade.  Yerkes  is  convinced,  from  analogy  with  the  effects 
of  other  stimuli,  that  this  is  due  to  a  stronger  contraction  on  the  side 
most  intensely  lighted  —  that  farthest  from  the  shadow.  This  would, 
of  course,  turn  the  medusa  back  into  the  shade. 

Thus  in  the  course  of  time  practically  all  the  medusa?  in  the  vessel 
will  be  found  in  the  shaded  region. 

In  the  behavior  of  Gonionemus  with  relation  to  light  there  are  evi- 
dently a  number  of  paradoxical  facts.  The  medusa  swims  toward  the 
source  of  light,  yet  tends  to  gather  in  shaded  regions.  It  goes  at  first 
toward  a  source  of  strong  light,  later  reverses  this  reaction.  It  moves 
toward  the  source  of  light  when  excited,  but  becomes  indifferent  when 
undisturbed.  Different  individuals  react  differently  to  the  same  con- 
ditions, and  the  same  individual  reacts  differently  at  different  times. 
We  have  here  an  excellent  illustration  of  the  fact  that  the  reactions  of 
organisms,  even  to  simple  agents,  depend  on  a  multiplicity  of  factors. 
If  we  could  study  the  medusa  in  the  natural  conditions  under  which  it 
lives,  and  if  we  knew  thoroughly  the  physiological  processes  taking  place 
within  it,  we  should  doubtless  find  all  these  peculiarities  explained, 
and  should  probably  discover  that  its  reactions  are  regulatory.  When 
we  carry  such  an  animal  to  the  laboratory  and  experiment  upon  it  there, 
it  is  like  removing  an  organ  from  the  body  and  studying  it  in  a  dissect- 
ing dish.  We  cannot  understand  its  activities  without  knowing  their 
relations  to  the  rest  of  the  body  —  to  the  environmental  conditions. 

9.     Behavior  of  Ccelenterates  with  Relation  to  Food 

The  behavior  of  organisms  is  largely  determined  by  the  relation  of 
the  environment  to  their  internal  physiological  processes.  In  no  field 
is  this  so  striking  as  in  the  relation  of  behavior  to  the  obtaining  of  ma- 
terial for  carrying  on  the  processes  of  metabolism.  Under  this  point  of 
view  come  the  reactions  of  organisms  with  reference  to  food,  and  to  the 
gases  necessary  for  respiration.  These  reactions  in  the  Ccelenterata  we 
shall  take  up  now. 

A.  Food  and  Respiratory  Reactions  in  Hydra 

Hydras  are  usually  found  in  the  upper  parts  of  a  vessel  of  water, 
near  the  surface.  This  is  not  due  to  a  reaction  to  gravity,  but  rather 
to  the  relative  quantity  of  oxygen  in  different  parts  of  the  water.  If 
an  experiment  is  arranged  in  such  a  way  that  the  lower  surface  of  the 
vessel  is  free  and  in  contact  with  air,  while  the  upper  is  not,  the  Hydras 
tend  to  gather  near  the  lower  surface  (Wilson,  1891).     Collecting  in 


BEHAVIOR  OF  CCELENTERATA  217 

oxygenated  regions  is  probably  brought  about  through  a  process  of 
trial,  the  organisms  wandering  irregularly  till  they  come  into  oxygen- 
ated regions  and  there  remaining.  If  the  water  is  allowed  to  become 
very  foul,  all  the  Hydras  soon  collect  at  the  very  upper  surface,  often 
in  contact  with  the  surface  film  itself. 

Let  us  now  examine  the  usual  behavior  of  Hydra  in  obtaining  food, 
as  described  by  Wagner  (1905).  As  we  have  seen,  the  undisturbed 
green  Hydra  changes  its  position  at  intervals,  thus  in  the  course  of  time 
exploring  thoroughly  all  the  region  about  it.  The  tentacles  of  the  green 
Hydra  are  comparatively  short,  so  that  such  exploring  movements  are 
needed.  In  the  colorless  Hydras  the  tentacles  are  often  excessively  long 
and  slender,  lying  in  coils  on  the  bottom,  and  almost  filling  the  sur- 
rounding waters  with  a  network  of  fine 
threads.  They  may  reach  three  or 
four  inches  in  length.  In  these  spe- 
cies changes  of  position  are  less 
frequent,  the  great  length  of  the 
tentacles  rendering  this  unnecessary. 
When  a  small  animal  comes  in  con- 
tact with  one  of  the  tentacles,  in  a 
typical  case  a  somewhat   complicated 

reaction  OCCUrS.      The  nematOCVStS    of,        Fig.  131.  — Hydra  endeavoring  to  swal- 
.  .  .  t  •   i         1  •        1    l°w  a  large  annelid.     Camera  drawing. 

the    region  with    which    the    animal 

comes  in  contact  are  shot  out,  causing  the  organism  to  cease  its  move- 
ments. The  tentacle  is  viscid  and  clings  to  the  animal.  Now  the 
tentacle  is  bent  toward  the  mouth.  At  the  same  time  the  other  ten- 
tacles bend  in  the  same  direction.  If  the  animal  is  a  large  one  and  is 
inclined  to  struggle,  the  other  tentacles  seize  it,  and  many  nematocysts 
are  shot  out  and  pierce  it,  so  that  the  organism  may  become  quite 
covered  with  these  structures.  An  insect  larva  which  was  rescued  from 
a  Hydra  at  this  stage  is  shown  in  Fig.  132,  B.  Meanwhile,  the  mouth 
becomes  widely  opened,  sometimes  before  the  prey  comes  in  contact 
with  it.  When  the  food  reaches  the  mouth,  the  tentacles  usually  release 
it  and  are  folded  slightly  back,  while  the  edges  of  the  mouth,  or  "lips," 
actively  work  up  over  the  food,  till  it  is  enveloped  and  passes  into  the 
cavity  of  the  body.  In  this  way  a  Hydra  often  takes  organisms  much 
larger  than  itself.  Figure  131  shows  such  a  case,  where  a  Hydra  en- 
deavored to  swallow  an  annelid  that  was,  at  a  moderate  estimate,  fifty 
times  its  own  bulk.  The  mouth  and  body  were  immensely  distended, 
and  the  worm  was  about  half  enveloped.  The  Hydra  seemed  then  to 
have  reached  its  utmost  limit,  and  the  process  stopped. 

We  now  wish  to  analyze  this  complicated  behavior,  determining  as 


2l8 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


far  as  possible  the  nature  and  causes  of  the  different  factors  which  make 
it  up.  We  may  ask  first,  What  is  the  cause  of  the  discharge  of  the 
nematocysts  ? 

Near  each  nematocyst  there  is  a  projecting  point,  the  cnidocil  (Fig. 
132,  el).  This  has  often  been  compared  to  a  trigger;  touching  the 
cnidocil  is  said  to  cause  discharge  of  the  nematocyst.  That  is,  it  is  sup- 
posed that  a  mechanical  stimulus  is  the  cause  of  the  discharge.  But 
experiment  does  not  bear  out  this  supposition.  Hydra  may  be  rubbed 
roughly  with  a  needle,  without  causing  discharge  of  the  nematocysts. 

Hard  organisms,  such  as  Os- 
tracods,  may  strike  against 
it  or  run  over  its  surface, 
brushing  against  many  cnido- 
cils,  yet  no  nematocysts  are 
discharged.  On  the  other 
hand,  various  chemicals 
readily  cause  discharge  of 
the  nematocysts;  a  solution 
of  methylene  blue  or  methyl 
green,  for  example,  produces 
this  effect  in  a  marked  de- 
gree. Apparently,  then, 
some  chemical  stimulus  must 
be  associated  with  the  me- 
chanical stimulus  in  order  to 

Fig.  132  -Nematocysts  and  their  action  in  Hydra.  cause  discharge  of  the  nema. 
A,  portion  of  a  tentacle,  showing  the  batteries  of  nema-  ° 

tocysts;    d.,    cnidocils.      B,  insect    larva   covered  with  tOCystS.  Chemical     Stimuli 

nematocysts  as  a  result  of  capture  by  Hydra.  of    Qne    SQrt    Qr     another    wjU 

doubtless  usually  be  received  from  the  organisms  which  serve  as  prey. 

To  what  is  the  remainder  of  the  behavior  due?  One  thing  which 
must  be  noticed  first  is  that  the  food  reaction  depends  upon  the  physio- 
logical condition  of  the  animal.  Not  all  Hydras  react  to  suitable 
food,  but  only  those  which  have  not  been  recently  fed.  It  is,  of  course, 
not  surprising  that  only  hungry  Hydras  should  eat.  Yet  this  brings  out 
the  important  point  that  the  behavior  is  not  an  invariable  reflex,  but 
depends  on  the  physiological  state  of  the  organism. 

When  the  animal  eats,  are  the  determining  factors  of  the  reaction 
mechanical  stimuli  or  chemical  stimuli?  Experiment  shows  that  me- 
chanical stimuli  alone  do  not  induce  the  food  reaction.  If  bits  of  filter 
paper,  or  ostracods  with  a  hard  shell,  are  brought  in  contact  with  the 
tentacles  or  the  mouth  of  a  hungry  Hydra,  they  are  not  swallowed.  But 
if  the  filter  paper  is  soaked  in  meat  juice,  or  if  the  ostracod  is  crushed, 


BEHAVIOR   OF  CCELENTERATA  219 

then  they  are  readily  swallowed.  A  chemical  stimulation  is  a  necessary 
factor  in  producing  the  reaction.  But  under  usual  conditions  the  chemi- 
cal alone  —  the  meat  juice  —  will  not  produce  the  food  reaction.  There 
must  be  a  combination  of  chemical  stimuli  (of  the  proper  character)  and 
of  mechanical  stimuli  before  the  reaction  is  induced. 

But  when  the  Hydra  is  very  hungry  —  when  it  has  starved  for  a  long 
time  —  then  a  suitable  chemical  stimulus  acting  alone  will  produce  the 
food  reaction.  Placed  in  a  solution  of  extract  of  beef  the  very  hungry 
Hydra  opens  its  mouth  widely  and  takes  in  the  fluid.  What  seems 
very  remarkable  is  that  a  solution  of  quinine  produces  this  effect  as  well 
as  does  extract  of  beef  (Wagner,  1905). 

Thus  the  food  reaction  is  throughout  dependent  upon  the  physio- 
logical condition  of  the  Hydra.  Hydras  that  are  not  hungry  will  not  eat 
at  all ;  moderately  hungry  specimens  will  take  the  solid  food  (chemical 
and  mechanical  stimuli) ;  very  hungry  ones  take  liquid  food  (chemical 
stimulus  alone).  Hungry  Hydras  show  still  further  modifications  in 
their  behavior,  compared  with  those  that  are  not  hungry.  As  we  have 
previously  seen,  they  frequently  contract  and  change  to  a  new  position 
and  even  move  about  from  place  to  place.  Wilson  (1891)  records  a 
remarkable  cycle  of  behavior  in  hungry  yellow  Hydras.  Hydras  usually 
remain,  as  we  have  seen,  in  the  upper  layers  of  the  water,  on  account 
of  the  oxygen  there  found.  But  when  the  Crustacea  on  which  the  ani- 
mals feed  have  become  very  scarce,  so  that  little  food  is  obtained,  Hydra 
detaches  itself,  and  with  tentacles  outspread  sinks  slowly  to  the  bottom. 
Here  it  feeds  upon  the  debris  composed  of  dead  organic  matter  which 
collects  at  the  bottom,  often  gorging  itself  with  this  material.  It  then 
moves  toward  the  light,  and  at  the  lighted  side  again  upward  to  the 
surface.  Here  it  remains  for  a  time,  then  sinks  again  and  feeds  upon 
the  material  at  the  bottom.  This  cycle  may  be  repeated  indefinitely, 
requiring  usually  some  days  for  its  completion. 

B.  Food  Reactions  in  Medusa 

The  food  reactions  have  been  studied  most  carefully  in  Gonione- 
mus.  In  this  animal,  as  we  have  seen,  there  is  a  definite  set  of  "  fish- 
ing" movements,  having  the  function  of  obtaining  food.  These  move- 
ments are  of  course  not  direct  reactions  to  food,  but  are,  so  far  'as  food 
is  concerned,  spontaneous  movements  of  the  animal.  If  food  is  brought 
near  a  resting  medusa,  this  sets  the  animal  to  moving.  If  a  piece  of 
fish  is  placed  at  one  side  of  the  medusa,  it  does  not  move  directly  toward 
the  food,  according  to  Yerkes  (1902  a).  After  a  few  seconds  the  ten- 
tacles nearest  the  food  begin  to  move  about  irregularly,  and  this  gives 


220  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

them  a  chance  to  find  the  food  if  it  is  very  near.  If  they  do  not  find  it, 
"there  soon  follows  a  general  contraction  or  series  of  contractions  of 
the  bell,  which  may  take  the  animal  either  toward  or  away  from  the 
source  of  the  stimulus."  Thus  the  medusa  is  induced  by  the  presence 
of  food  to  swim  about,  and  it  usually  in  this  way  sooner  or  later  comes 
in  contact  with  the  food  (Yerkes,  1902  a,  p.  438).  The  behavior  is 
throughout  not  a  definitely  directed  action,  but  an  excellent  example 
of  the  method  of  trial  —  of  what  we  call  searching,  in  higher  animals. 

When  the  tentacles  actually  come  in  contact  with  food,  they  con- 
tract and  twist  about  each  other  in  such  a  way  as  to  hold  it.  The  group 
of  contracting  tentacles  then  bends  toward  the  mouth,  and  that  portion 
of  the  margin  of  the  bell  bearing  them  contracts,  drawing  them  nearer 
the  mouth.  The  manubrium  bends  toward  the  food,  placing  the  mouth 
against  it,  and  the  food  is  enveloped  by  the  lips  and  swallowed. 

What  are  the  determining  factors  in  this  behavior?  Doubtless,  as 
in  Hydra,  internal  conditions  play  a  part  in  determining  the  reaction  to 
food  bodies,  but  this  matter  has  not  been  studied  in  the  medusa.  As 
to  external  factors,  Yerkes  (1902  a)  has  brought  out  the  following:  In 
Gonionemus  the  entire  food  reaction  may  be  produced  by  chemicals 
alone.  If  with  a  pipette  a  strong  infusion  of  fish  meat  is  applied  to  the 
tentacles,  they  twist  and  contract,  bending  toward  the  mouth,  while  the 
manubrium  as  usual  bends  toward  the  tentacles  stimulated.  Solutions 
of  common  inorganic  chemicals  do  not  produce  this  result ;  the  tentacles 
merely  contract  from  them,  remaining  straight.  If  the  infusion  of  fish 
meat  is  made  very  weak,  the  animal  begins  the  food  reaction,  contract- 
ing and  twisting  the  tentacles ;  but  the  reaction  goes  no  farther.  In  rare 
cases  Yerkes  (1902  a,  p.  439)  found  that  the  animal  begins  the  food  re- 
action when  a  very  weak  inorganic  chemical,  such  as  an  acid,  is  applied 
to  it.  But  this  quickly  ceases,  before  it  has  gone  far.  The  medusa  in 
such  cases  makes  what  we  call  in  higher  animals  a  mistake,  but  changes 
its  behavior  as  soon  as  it  discovers  the  mistake. 

Mechanical  stimuli  of  a  certain  sort  may  likewise  produce  the  food 
reaction.  With  regard  to  this  we  find  in  Gonionemus  certain  peculiar 
and  most  suggestive  relations. 

If  riie  tentacles  come  in  contact  with  some  quiet  object,  or  are  touched 
with  a  rod  or  a  needle,  they  merely  contract,  remaining  straight,  as 
when  they  are  affected  by  inorganic  chemicals.  The  response  is  clearly 
a  negative  reaction,  not  a  food  reaction.  But  if  the  tentacles  are  touched 
in  a  peculiar  way,  by  drawing  the  rod  quickly  across  them,  they  behave 
differently.  They  quickly  react  and  twist,  just  as  when  they  touch  a 
piece  of  meat.  Then  they  bend  toward  the  mouth,  the  margin  bearing 
them  contracting  inward  as  usual,  while  the  manubrium  bends  toward 


BEHAVIOR  OF   CCELENTERATA  221 

them.  Finding  no  food,  the  swallowing  movements  of  the  manu- 
brium do  not  occur.  Thus  "motile  touch,"  as  Yerkes  (1902  a)  calls  it, 
causes  the  food  reaction,  while  the  touch  of  an  object  that  is  at  rest 
causes  only  a  negative  reaction.  This  reaction  to  a  moving  object 
shows  clearly  the  adaptation  of  the  behavior  to  the  natural  conditions 
of  life.  Usually,  when  something  moves  quickly  along  the  tentacles  of 
a  medusa,  this  will  be  a  fish  or  other  small  animal,  well  fitted  to  serve 
as  food.  So  the  medusa  reacts  to  such  a  moving  thing  in  such  a  way 
as  to  seize  it  and  bear  it  to  its  mouth.  If  the  object  turns  out  not  to  be 
good  for  food,  as  is  rarely  the  case,  there  is  of  course  no  harm  done, 
and  it  may  be  rejected.  If  the  medusa  comes  in  contact  with  an  ob- 
ject that  is  not  moving,  this  will  probably  be  a  stone  or  plant  or  other 
object  not  fit  for  food,  hence  the  animal  makes  no  attempt  to  take  it. 
The  behavior  is  based,  at  it  were,  on  the  probability  that  any  given 
case  will  correspond  to  the  usual  condition.  Movement  serves  to  the 
medusa  as  a  sign  of  something  living  and  fit  for  food,  just  as  it  does  to 
hunters  among  higher  animals  and  even  among  men.1  It  is  a  most  in- 
teresting fact  that  the  positive  reaction  to  a  moving  object  is  more  rapid 
than  to  a  quiet  one,  even  though  the  latter  is  actually  food,  while  the 
former  is  not.  The  reaction  time  for  a  moving  object  was  found  by 
Yerkes  (1902  a,  p.  440)  to  be  about  0.30  to  0.35  seconds,  while  the 
reaction  time  for  quiet  objects  or  food  is  0.40  to  0.50.  This  is  again 
directly  adapted  to  usual  conditions ;  to  a  moving  animal  reaction  must 
be  rapid,  or  it  is  useless.  One  can  hardly  do  otherwise  than  hold  that 
this  specialized  reaction  to  moving  objects,  so  appropriate  to  the  natural 
conditions  of  the  animal,  is  not  a  primitive  reflex,  but  must  have  been 
historically  developed  in  some  way,  and  that  it  would  not  occur  if  it 
were  not  in  the  long  run  beneficial. 

C.  Food  Reactions  in  Sea  Anemones 

In  sea  anemones  the  dependence  of  the  reactions  toward  food  and 
other  agents  on  the  physiological  state  of  the  animal,  particularly  as 
determined  by  the  progress  of  metabolism,  is  very  striking. 

Finding  Food.  —  Sea  anemones  remain  for  the  most  part  quiet,  with 
disk  and  tentacles  outspread,  depending  for  food  largely  on  the  acci- 
dental contact  of  moving  organisms  with  these  organs.     But  there  are 

1  In  this,  as  in  other  cases,  such  expressions  as  "serves  as  a  sign"  of  course  does  not 
affirm  a  mental  sign,  concerning  which  we  have  no  knowledge  in  animals  outside  of  the 
self.  It  signifies  merely  that  movement  does,  as  a  matter  of  fact,  cause  a  reaction  which 
is  appropriate  to  something  usually  accompanying  the  motion,  so  that  the  behavior  is 
objectively  identical  with  that  due  in  higher  animals  and  man  to  a  stimulus  that  serves  as 
a  sign. 


222  BEHAVIOR   OF    THE  LOWER   ORGANISMS 

certain  active  movements  which  assist  in  procuring  food.  In  most  sea 
anemones  light  stimulation  of  the  tentacles,  however  produced,  causes 
these  organs  to  wave  back  and  forth,  just  as  happens  in  medusae ;  this 
increases  the  chances  of  coming  in  contact  with  food.  In  Sagartia,  ac- 
cording to  Torrey,  the  presence  of  food  near  one  side  of  the  animal, 
resulting  in  weak  chemical  stimulation,  gives  rise  to  more  definite  move- 
ments. Part  of  the  tentacles  bend  toward  the  food,  contracting  on  the 
side  most  strongly  stimulated,  while  others  bend  toward  the  mouth.  The 
animal  may  at  times  bend  its  body  toward  the  food,  thus  securing  it. 
The  tendency  of  the  tentacles  to  bend  toward  the  mouth,  as  if  carrying 
food,  when  stimulated  in  almost  any  way,  is  very  striking  in  many 
ccelenterates.  In  Sagartia  the  tentacles  when  touched  bend  first  toward 
the  side  stimulated,  then  toward  the  mouth.  In  the  hydroid  Cory- 
morpha,  according  to  Torrey  (1904  a),  the  tentacles  when  thus  stimulated 
bend  only  toward  the  mouth.  This  bending  toward  the  mouth  of  course 
serves  the  function  of  carrying  food,  and  it  seems  to  have  become  the 
reaction  to  all  sorts  of  stimuli,  on  the  chance,  as  it  were,  that  it  will  serve 
this  function,  in  the  given  case.  The  plan  of  the  behavior  is  that  of 
trial  of  a  reaction  that  is  beneficial  under  most  circumstances. 

The  Taking  of  Food.  —  In  the  actual  taking  of  food  the  behavior 
varies  greatly  in  different  sea  anemones.  In  some  species  ciliary  move- 
ment plays  the  chief  part  in  the  process,1  though  assisted  by  muscular 
contractions.  In  others,  bodily  movements  brought  about  by  muscles 
are  the  main  factors.  Two  or  three  examples  will  illustrate  the  principal 
variations  in  this  matter. 

The  common  Metridium  marginatum  of  the  east  coast  of  the  United 
States  is  an  example  of  the  species  in  which  ciliary  movement  is  perhaps 
the  chief  agent  in  food-taking.  Under  usual  conditions  the  tentacles  are 
pointed  away  from  the  mouth,  and  are  covered  with  cilia,  which  beat 
toward  the  tip  of  the  tentacle.  Thus  small  particles  falling  on  the  ten- 
tacles are  carried  outward  by  the  cilia  and  removed  from  the  animal. 
But  if  the  particle  is  something  fit  for  food,  the  behavior  is  changed. 
When  a  bit  of  crab's  flesh  is  dropped  among  the  tentacles,  they  contract 
on  the  side  touched,  thus  grasping  the  flesh.  They  then  bend  inward, 
arching  over  with  tips  toward  the  mouth.  The  cilia,  continuing  to  strike 
toward  the  tip,  now  of  course  carry  the  food  toward  the  mouth  instead 
of  away  from  it.  In  time  the  meat  drops  from  the  tip  of  the  tentacles 
into  or  near  the  mouth. 

The  inner  surface  of  the  oesophagus,  or  tube  into  which  the  mouth 
leads,  is  covered  with  cilia,  which  beat  outward  (save  in  the  two  grooves 
at  the  angles,  known  as  the  siphonoglyphes).     They  thus  bear  outward 

1  For  details  regarding  this  for  many  different  species,  see  Carlgren,  1905. 


BEHAVIOR   OF  CCELENTERATA  223 

any  indifferent  particles  which  may  fall  in  the  oesophagus.  But  when  a 
piece  of  meat  is  dropped  into  the  mouth,  the  cilia  at  once  reverse,  now 
beating  inward.  They  thus  carry  the  food  into  the  digestive  cavity  of 
the  animal. 

Meanwhile,  the  muscles  surrounding  the  mouth,  and  those  of  the 
oesophageal  tube,  contract  in  such  a  way  as  to  produce  swallowing  move- 
ments, which  aid  in  ingesting  the  food.  These  swallowing  movements 
may  begin  while  the  food  is  still  held  by  the  tentacles,  showing  that  the 
stimulation  from  the  food  has  been  transmitted. 

In  Aiptasia  annulata  there  are  cilia  which  act  in  the  same  manner 
as  in  Metridium,  but  the  chief  role  in  food-taking  is  played  by  move- 
ments of  the  tentacles  and  oesophagus.  If  a  small  object  comes  in  con- 
tact with  a  tentacle,  it  adheres  to  the  surface,  and  the  tentacle  contracts 
strongly,  the  entire  animal  usually  contracting  at  the  same  time.  Then 
the  tentacle  bends  over  and  places  the  food  with  considerable  precision 
on  the  mouth.  The  adjacent  tentacles  likewise  bend  over  and  are  ap- 
plied to  the  food  body,  holding  it  down  against  the  mouth.  The  latter 
then  opens,  the  lips  seizing  the  food,  while  the  tentacles  may  release  it 
and  bend  away.  The  swallowing  of  the  food  is  mainly  due  to  the  activi- 
ties of  the  lips  and  oesophagus.  In  this  animal  a  bit  of  food  may  be 
completely  enclosed  within  ten  seconds  of  the  time  it  touches  a  tentacle. 

In  the  large  sea  anemone  Stoichactis  helianthus,  cilia  seem  to  play 
no  part  in  the  taking  of  food.  In  this  animal  the  disk  may  be  10  to 
15  cm.  in  diameter.  If  a  piece  of  crab  meat  is  placed  on  the  disk 
of  a  hungry  specimen,  the  tentacles  immediately  surrounding  it  be- 
gin suddenly  to  wave  back  and  forth.  This  movement  stops  for  a 
few  seconds,  then  begins  again.  All  the  tentacles  that  come  in  contact 
with  the  food  bend  over  against  it  and  shrink,  so  as  to  hold  it  down 
against  the  disk.  Now  that  portion  of  the  disk  bearing  the  food  begins 
to  sink  inward,  the  mouth  begins  to  open,  and  the  walls  of  the  oesopha- 
gus protrude  from  the  mouth  as  large  bladderlike  lobes.  The  region 
between  the  mouth  and  the  food  contracts,  the  tentacles  which  it  bears 
collapsing  and  almost  completely  effacing  themselves.  By  this  con- 
traction the  mouth  and  food  are  caused  to  approach  each  other,  the 
intervening  region  almost  disappearing.  The  oesophageal  lobes  in- 
crease in  size,  becoming  3  or  4  cm.  long  and  half  as  thick;  they 
extend  toward  the  food,  finally  reaching  it.  The  mouth  may,  in  the 
way  described,  be  transferred  from  the  centre  of  a  disk  10  cm.  in 
diameter  to  within  1  cm.  of  the  edge.  Now  the  oesophageal  lobes 
extend  over  the  food,  while  the  tentacles  progressively  withdraw  from 
it,  till  the  food  is  lying  on  the  contracted  part  of  the  disk,  completely 
covered  by  the  oesophageal  lobes.     Now  that  part  of  the  disk  below  the 


224  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

food  withdraws,  by  an  extension  and  displacement  of  the  mouth,  till 
there  is  nothing  beneath  the  food  body,  and  it  is  pressed  by  the  oeso- 
phageal lobes  into  the  internal  cavity.  The  lobes  then  withdraw  and 
the  mouth  closes. 

The  determining  factors  in  the  food  reaction  are  partly  internal, 
partly  external,  the  variations  of  the  former  playing  perhaps  the  most 
important  part.  Many  of  the  sea  anemones  are  voracious,  taking  food 
until  the  body  forms  a  distended  sac.  But  in  most  species,  if  not  all, 
the  behavior  changes  decidedly  as  the  animal  becomes  less  hungry,  and 
after  a  time  it  refuses  to  take  food,  even  removing  it  if  the  food  is  ap- 
plied to  the  disk.  The  changes  in  reaction  as  hunger  decreases  seem 
less  marked  in  those  species  in  which  the  food  is  taken  mainly  by  ciliary 
action. 

Specimens  that  have  not  been  fed  for  a  long  period  frequently  swallow 
indifferent  bodies,  such  as  pellets  of  paper,  grains  of  sand,  and  the  like. 
This  has  been  observed  in  Aiptasia  (Jennings,  1905  a),  Sagartia  (Torrey, 
1904),  Metridium  (Allabach,  1905),  and  in  a  number  of  Mediterranean 
anemones  (Nagel,  1892).  In  Stoichactis  the  taking  of  such  indifferent 
bodies  is  rare,  but  sometimes  occurs.  In  Sagartia  and  Metridium  such 
indifferent  bodies  cause  a  reversal  of  the  beat  of  the  oesophageal  cilia, 
just  as  is  occasioned  by  actual  food.  All  together,  it  is  clear  that  in 
hungry  specimens  of  various  sea  anemones  mechanical  stimuli  acting 
alone  may  cause  the  food  reaction. 

In  some  cases  chemical  stimuli  acting  alone  produce  the  food  re- 
action. If  filtered  crab  juice  is  applied  to  the  tentacles  of  Metridium, 
they  arch  over  toward  the  mouth.  If  the  juice  reaches  the  mouth,  the 
cilia  of  the  oesophagus  are  reversed,  striking  inward,  just  as  when  a 
piece  of  meat  is  present.  The  swallowing  movements  of  the  oesopha- 
gus may  likewise  take  place  under  chemical  stimulation.  Parker  (1905) 
has  lately  found  that  certain  inorganic  chemicals,  containing  potassium, 
will  cause  the  cilia  to  reverse  and  beat  inward ;  this  is  the  case  for  ex- 
ample, with  KC1  and  KN03.  But  the  reversal  which  takes  place  under 
the  action  of  meat  juice  is  not  due  to  the  potassium  salts  which  it  con- 
tains, for  it  requires  a  concentration  of  the  potassium  salt  to  produce 
this  result  that  is  much  greater  than  that  existing  in  meat  juice.  In 
Adamsia,  according  to  Nagel  (1892),  the  tentacles  react  to  sugar  in  the 
same  way  as  to  meat  juice;  this  is  not  true  for  Metridium  and  Sagartia. 

As  sea  anemones  become  less  hungry  they  usually  cease  to  react  to 
such  indifferent  bodies  as  grains  of  sand,  pellets  of  paper,  etc.,  though 
they  still  take  crab  meat  readily.  In  Metridium  and  Sagartia  bits  of 
paper  no  longer  cause  the  reversal  of  the  oesophageal  cilia,  by  which 
particles  are  carried  to  the  mouth,  while  crab  meat  still  produces  this 


BEHAVIOR   OF   CCELENTERATA  225 

effect.  In  Aiptasia  annulata  the  tentacles  no  longer  carry  pellets  of 
paper  to  the  mouth,  but  bend  backward  along  the  column  and  drop 
them.  In  the  Stoichactis  that  is'not  very  hungry  such  indifferent  bodies 
are  removed  by  the  rejecting  reaction  described  on  page  202. 

As  the  sea  anemones  become  still  less  hungry  the  reaction  to  even 
such  food  bodies  as  pieces  of  crab  meat  becomes  changed.  The  reaction 
gradually  becomes  slower  and  less  precise.  In  a  hungry  specimen  of 
Aiptasia  the  food  reaction  is  rapid,  often  requiring  but  ten  or  fifteen 
seconds.  But  after  several  pieces  of  meat  have  been  taken,  the  reaction 
occupies  a  much  longer  period.  The  tentacles  touched  by  the  food  may 
not  react  for  several  seconds,  then  they  bend  in  a  languid  way  toward 
the  centre  of  the  disk,  while  the  adjacent  tentacles  may  not  react  at  all. 
The  food  body  is  not  placed  so  accurately  on  the  mouth  as  before.  At 
a  later  stage  food  applied  to  the  tentacles  induces  no  reaction  at  all,  or 
a  withdrawal  of  the  tentacles,  while  if  it  is  applied  directly  to  the  mouth 
it  is  very  slowly  swallowed.  In  Stoichactis  at  this  stage  food  is  often 
carried  toward  the  mouth,  then  after  or  even  before  it  reaches  the  mouth 
the  reaction  is  reversed  and  the  food  is  rejected.  If  two  pieces  of  meat 
are  applied  at  once  to  the  disk  of  Stoichactis  when  in  this  condition,  one 
may  be  swallowed  while  the  other  is  rejected.  Often  in  Aiptasia  one 
piece  may  be  rejected,  while  the  immediately  following  piece  is  swal- 
lowed. The  animal  seems  in  a  condition  of  most  unstable  equilibrium, 
so  that  the  reactions  are  most  inconstant  and  variable.  No  one  could 
suppose,  in  studying  the  behavior  of  a  sea  anemone  in  this  condition, 
that  the  behavior  of  such  organisms  is  made  up  of  invariable  reflexes, 
always  occurring  in  the  same  way  under  the  same  external  conditions. 

As  the  animal  becomes  satiated,  the  food  reaction  ceases  completely. 
Pieces  of  crab  meat  placed  on  the  disk  of  a  Stoichactis  in  this  state  are 
removed  by  the  rejecting  reaction  already  described.  Aiptasia  either 
does  not  react  at  all  when  food  is  applied  to  the  tentacles,  or  the  ten- 
tacles contract  and  bend  backward  —  a  negative  reaction. 

Some  anemones  are  exceedingly  voracious,  seeming  to  take  food  as 
long  as  it  is  mechanically  possible  for  them  to  do  so.  This  seems  to 
be  the  case,  for  example,  with  Metridium,  where  the  changes  in  reaction 
as  the  animal  becomes  filled  with  food  are  almost  lacking.  It  may  feed 
till  the  body  cavity  becomes  so  completely  filled  as  to  cause  disturbance 
of  function.  As  a  result  the  entire  mass  of  food  is  sometimes  disgorged 
undigested.  After  this  has  occurred,  Metridium  will  often  take  food  as 
before.  But  in  most  sea  anemones  the  taking  of  food  ceases  before  any 
such  disturbance  has  been  produced. 

The  rejection  of  food  is  not  determined  merely  by  the  mechanical 
fulness  of  the  digestive  cavity,  but  is  evidently  due  to  the  effects  of  food 

Q 


226  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

on  the  internal  processes.  An  Aiptasia  (species  undetermined),  studied 
by  the  present  author,  continued  to  take  filter  paper  till  the  body  was  a 
swollen  sack,  and  pieces  of  the  paper  were  repeatedly  disgorged.  But 
new  pieces,  and  even  those  that  had  just  been  disgorged,  were  readily 
swallowed  when  applied  to  the  disk.  But  when  specimens  of  this 
Aiptasia  were  fed  considerable  quantities  of  meat,  they  refused  to  take 
either  more  meat  or  paper. 

The  reactions  of  well-fed  sea  anemones  differ  in  many  other  ways 
from  those  of  hungry  specimens.  They  are  much  less  inclined  to  react 
to  stimuli  of  all  sorts.  A  disturbance  in  the  water,  or  a  touch  with  a 
needle,  that  would  produce  a  strong  contraction  in  the  hungry  animal, 
often  causes  no  reaction  whatever  in  the  satiated  specimen.  A  much 
stronger  solution  of  any  given  chemical  is  required  to  produce  contrac- 
tion than  in  the  well-fed  individual.  If  we  should  attempt  to  determine 
the  strength  of  a  given  chemical  that  caused  contraction  in  Aiptasia,  we 
should  get  totally  different  results,  according  as  we  employed  specimens 
that  were  very  hungry,  or  only  moderately  hungry,  or  thoroughly  satiated. 

Another  factor  influencing  the  food  reactions  of  the  sea  anemone  is 
fatigue,  and  the  effects  due  to  this  are  easily  mistaken  for  phenomena 
of  a  different  character.  If  the  tentacles  of  a  certain  region  of  the  disk 
of  Metridium  are  given  many  pieces  of  food,  one  after  the  other,  they 
refuse  after  a  time  to  take  the  food,  though  the  other  tentacles  will  still 
take  food  readily.  In  taking  food  very  large  quantities  of  mucus  are 
produced,  and  it  is  not  surprising  that  many  rapid  repetitions  of  this 
process  exhaust  the  tentacles.  If  they  are  allowed  to  rest  five  to  ten 
minutes,  they  usually  take  food  as  at  first. 

As  the  fatigue  conies  on,  the  tentacles  first  cease  to  react  to  weak 
stimuli,  such  as  are  produced  by  plain  paper,  or  paper  soaked  in  meat 
juice ;  later  to  strong  stimuli,  such  as  that  produced  by  meat.  If  meat 
and  paper  are  given  in  alternation,  the  tentacles  will  thus  at  first  take 
both ;  then  they  come  to  refuse  the  paper,  while  the  meat  is  still  taken. 
Later  they  come  to  refuse  the  meat  also. 

The  reaction  to  food  varies  also  with  certain  other  conditions.  In 
Metridium  and  Aiptasia  the  following  is  often  observed:  A  specimen 
refuses  to  take  bits  of  filter  paper,  though  it  still  takes  meat.  After  it 
has  thus  refused  paper,  two  or  three  pieces  of  meat  are  given  in  succes- 
sion, and  taken  readily.  Now  the  bit  of  paper  is  placed  again  on  the 
disk,  and  it  too  is  swallowed.  Clearly,  the  uninterrupted  taking  of  a 
number  of  pieces  of  meat  changes  the  physiological  condition  in  some 
way,  preparing  the  animal  for  the  taking  of  any  object  with  which  it 
comes  in  contact.  One  cannot  fail  to  note  the  parallelism  with  what 
occurs  in  higher  animals  under  similar  conditions. 


BEHAVIOR   OF   CCELENTERATA  227 

10.    Independence  and  Correlation  of  Behavior  of  Different 

Parts  of  the  Body 

There  is  a  general  agreement  among  those  who  have  studied  the 
behavior  of  coelenterates  that  the  different  parts  of  the  body  show  re- 
markable independence  in  their  reactions.  The  tentacles  of  the  sea 
anemones  and  medusae  react  to  most  stimuli  in  essentially  the  same 
manner  when  cut  off  from  the  body  as  when  attached.  The  isolated 
tentacles  of  Gonionemus  react  to  meat  juice  by  contracting  and  twist- 
ing, as  in  the  usual  food  reaction,  while  to  inorganic  chemicals  they  react 
by  a  straight  contraction,  as  in  the  negative  reaction  of  the  medusa 
(Yerkes,  1902  b,  p.  183).  In  Sagartia  (Torrey,  1904)  and  Metridium 
(Parker,  1896)  the  separate  tentacles  react  to  meat  juice  by  bending 
toward  the  side  which  formerly  looked  toward  the  mouth.  Thus 
each  tentacle  must  contain  within  itself  the  apparatus  necessary  for  its 
usual  reactions. 

The  fact  that  the  tentacles  have  their  own  reactions  independently  of 
the  rest  of  the  body  is  illustrated  in  a  curious  way  in  Loeb's  experiment 
on  heteromorphosis  in  Cerianthus  (Loeb,  189 1).  He  succeeded  in 
causing  tentacles  to  develop  at  one  side  of  the  animal,  forming  a  group 
not  associated  with  a  mouth.  These  tentacles  reacted  to  food  as  usual, 
seizing  upon  it,  and  bending  over  with  it  in  the  direction  in  which, 
under  normal  conditions,  a  mouth  would  be  found.  Here  it  was  pressed 
down  for  a  time,  then  released. 

Like  the  tentacles,  other  parts  of  the  body  may  react  independently. 
Yerkes  (1902  b)  cut  off  the  manubrium  of  Gonionemus  and  pinned  it 
by  its  base  to  the  bottom  of  a  dissecting  dish.  It  now  bent  toward  food, 
seized  upon  and  swallowed  it,  just  as  in  the  uninjured  medusa.  Many 
experiments  with  similar  results  are  described  in  the  work  of  Romanes 
(1885).  Parker  (1896)  isolated  a  small  bit  of  the  ciliated  epithelium 
of  the  oesophagus  of  Metridium.  He  found  that  this  reacted  to  meat 
juice  by  a  reversal  of  the  ciliary  stroke,  just  as  happens  in  the  uninjured 
animal.  In  Actinia,  Loeb  (1891)  found  that  if  the  head  is  cut  off,  the 
lower  part  of  the  animal  will  take  food  through  the  oesophageal  opening. 
If  the  animal  is  cut  in  two,  even  the  open  lower  end  of  the  upper  half 
will  take  food,  just  as  will  the  mouth. 

For  experiments  of  this  kind,  the  bell  of  the  medusa  has  become, 
through  the  work  of  Romanes  (1885),  a  classical  object.  Separating 
the  margin  of  the  bell,  containing  the  chief  portion  of  the  nervous  sys- 
tem, from  the  central  part,  has  been  a  favorite  experiment.  Romanes 
found  that  in  the  Hydromedusse  the  margin  continues  to  beat  rhythmi- 
cally, while  the  centre  usually  ceases  its  spontaneous  movement.     But 


228  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

this  was  not  due  to  any  actual  inability  of  the  centre  to  initiate  move- 
ment, for  Romanes  found  that  when  it  was  stimulated  in  various  ways, 
it  contracts  rhythmically.  This  occurred  in  the  centre  of  the  bell  of 
Sarsia  when  placed  in  certain  chemicals,  notably  in  weak  acids,  and 
in  a  glycerine  solution  (Romanes,  1885,  pp.  190-197).  Rhythmical 
contractions  have  likewise  been  observed  by  Loeb  (1900  a)  in  the  iso- 
lated centre  of  Gonionemus  when  placed  in  a  pure  solution  of  sodium 
chloride.  Thus  it  is  clear  that  not  only  the  margin,  containing  the 
greater  part  of  the  nervous  system,  but  also  the  centre  of  the  bell,  has 
the  power  of  contracting  rhythmically. 

These  and  many  other  experiments  have  shown  that  each  part  of 
the  body  has  in  the  ccelenterates  certain  characteristic  ways  of  reacting 
to  stimuli,  and  that  it  may  react  in  these  ways  even  when  separated 
from  the  rest  of  the  body.  Its  reactions  may  be  determined  within 
itself.  But  from  this  the  conclusion  cannot  be  drawn  that  the  behavior 
of  these  animals  consists  entirely  of  the  separate  and  independent  re- 
actions of  these  parts  to  external  stimuli.  While  each  part  may  react 
independently,  each  may  also  react  with  reference  to  influences  coming 
from  other  parts  of  the  body.  Thus,  the  tentacles  may  react,  not  only 
to  external  stimuli  directly  impinging  upon  them,  but  also,  in  many 
ccelenterates  at  least,  to  stimuli  that  are  transmitted  from  other  parts. 
A  strong  stimulus  on  the  body  or  on  a  single  tentacle  causes  a  contrac- 
tion of  many  tentacles.  In  some  cases  this  contraction  of  the  other 
tentacles  appears  to  be  due  to  a  direct  spreading  of  the  muscular  con- 
traction. One  fibre  pulls  on  another,  setting  it  in  action,  until  the  pull 
reaches  the  base  of  the  tentacle.  This  pull  then  acts  as  a  direct  stimu- 
lus, causing  the  tentacle  to  contract,  in  the  same  way  that  would  occur 
if  it  were  mechanically  stimulated  from  outside.  This  is  the  way  in 
which  Torrey  conceives  of  the  matter  in  Sagartia.  If  this  is  the  correct 
explanation,  there  is  of  course  nothing  comparable  to  nervous  trans- 
mission —  passage  of  a  wave  of  stimulation  independently  of  a  wave  of 
contraction  —  in  these  cases. 

In  Aiptasia  annulata,  on  the  other  hand,  a  light  stimulus  on  the  tip 
of  one  of  the  long  tentacles  induces  a  sudden  quick  contraction  of  the 
entire  body.  This  contraction  appears  to  the  eye  to  take  place  over 
the  entire  body  at  once,  and  it  is  so  rapid  as  to  suggest  strongly  the  opera- 
tion of  a  conducting  nervous  system.  The  well-known  experiments  of 
Romanes  (1885,  p.  76)  demonstrated  completely  that  in  medusae  there 
is  such  a  wave  of  stimulation  independent  of  a  wave  of  contraction, 
and  that  this  wave  of  stimulation  coming  from  other  parts  of  the  body 
causes  the  tentacles  to  contract.  By  cutting  off  the  margin  of  Aurelia 
in  the  form  of  a  long  strip  and  stimulating  one  end,  he  could  cause  a 


BEHAVIOR   OF   CCELENTERATA  229 

wave  of  stimulation  to  pass  to  the  opposite  end.  This  wave  of  stimu- 
lation was  followed,  if  the  stimulus  was  intense,  by  a  wave  of  contrac- 
tion ;  if  the  stimulus  was  weak,  the  wave  of  stimulation  passed  alone. 
This  wave  caused  the  tentacles  along  the  margin  to  contract  as  it 
reached  them. 

Furthermore,  we  have  seen  above  that  the  reaction  of  the  tentacles 
or  of  other  parts  of  the  body  to  a  given  stimulus  depends  upon  the  gen- 
eral physiological  state  of  the  body,  as  determined  by  the  progress  of 
metabolism.  Certain  tentacles  may,  through  the  activity  of  totally 
different  tentacles,  in  another  region  of  the  body,  in  supplying  material 
for  the  metabolic  processes,  come  to  react  to  a  given  stimulus  in  a  man- 
ner entirely  different  from  their  former  reactions. 

The  tentacles  are  therefore  not  to  be  compared  exclusively  to  in- 
dependent organisms  associated  in  a  group,  but  they  form  parts  of  a 
unified  organism.  While  they  may  react  when  isolated,  they  react  also 
under  the  influence  of  other  parts  of  the  body.  We  have  of  course  the 
same  condition  of  affairs  in  the  muscles  and  various  other  organs  of 
vertebrates.  They  may  react  when  isolated,  but,  like  the  tentacles 
of  the  medusa,  they  likewise  react  to  influences  coming  from  other  parts 
of  the  organism. 

The  same  is  true  for  the  manubrium  and  for  other  parts  of  the  body. 
While  the  isolated  manubrium  of  Gonionemus  may  react  by  bending 
toward  food,  it  shows  the  same  reaction  when  certain  of  the  tentacles 
are  stimulated  by  an  object  moving  rapidly  across  them.  The  varied 
reactions  of  the  manubrium  to  influences  affecting  other  parts  of  the  body 
are  shown  most  clearly  in  the  experiments  of  Romanes  described  on 
page  201.  In  Hydra,  when  the  tentacles  have  seized  food,  the  mouth 
often  begins  to  open  long  before  the  food  has  reached  it.  In  Metridium, 
according  to  Parker,  when  the  tentacles  are  touched  by  food,  the 
oesophagus  frequently  shows  peristaltic  contractions,  and  the  sphincter  of 
the  mouth  closes.  It  is  clear  that  there  is  a  definite  coordination  and 
unity  in  the  behavior,  brought  about  by  a  transmission  of  stimuli  from 
one  part  of  the  body  to  another.  The  difference  between  these  organisms 
and  higher  animals  is  in  this  respect  only  one  of  degree.  In  the  ccelen- 
terates  a  large  share  of  the  behavior  is  due  to  the  independent  reactions 
of  the  different  organs  to  the  external  stimuli,  and  the  transmission  of 
influences  from  one  part  of  the  body  to  another  takes  place  slowly  and 
without  such  precision  as  we  find  in  higher  animals. 

The  part  played  by  the  nervous  system  in  unifying  the  body  we 
need  not  take  up  here,  as  it  has  been  thoroughly  analyzed  in  the  brill- 
iant work  of  Romanes  (1885),  and  has  been  further  discussed  by  Loeb 
(1900).     The  essential  conclusion  to  be  drawn  from  the  experiment::! 


230  BEHAVIOR  OF   THE  LOWER  ORGANISMS 

results  seems  to  be  as  follows :  The  nervous  system  forms  a  region  in 
which  the  physiological  changes  resulting  in  activity  take  place  more 
readily  and  rapidly  than  in  other  parts  of  the  protoplasm.  These 
changes  occur  in  the  nervous  system  more  readily  both  as  a  result  of  the 
action  of  external  stimuli,  and  under  the  influence  of  changes  in  neigh- 
boring parts  of  the  body.  Hence  parts  containing  the  nervous  system 
are  more  sensitive  to  external  stimulation  than  other  parts  of  the  body, 
and  they  serve  to  transmit  stimulation  more  readily.  Furthermore, 
the  spontaneous  changes  occurring  in  the  protoplasm,  which  result  in 
the  production  of  rhythmical  contractions,  are  more  pronounced  and 
rapid  in  the  nervous  system  than  elsewhere,  so  that  the  rhythmical 
contractions  usually  begin  in  parts  containing  nerve  cells.  But  the 
difference  between  nerve  cells  and  other  cells  is  only  quantitative  in 
character.  The  peculiar  properties  of  the  nerve  cells  are  properties  of 
protoplasm  in  general,  but  somewhat  accentuated. 

11.     Some  General  Features  of  Behavior  in  Ccelenterates 

Comparing  the  behavior  of  this  low  group  of  multicellular  animals 
with  that  of  the  Protozoa,  we  find  no  radical  difference  between  the  two. 
In  the  ccelenterates  there  are  certain  cells  —  the  nerve  cells  —  in  which 
the  physiological  changes  accompanying  and  conditioning  behavior 
are  specially  pronounced,  but  this  produces  no  essential  difference  in 
the  character  of  the  behavior  itself.  As  in  the  Protozoa,  so  here,  we 
find  behavior  based  largely  on  the  process  of  performing  continued  or 
varied  movements  which  subject  the  organism  to  different  conditions 
of  the  environment,  with  selection  of  some  and  rejection  of  others. 
We  find  the  same  changes  in  behavior  under  a  continued  intense  stimu- 
lus, determined  by  changes  in  the  physiological  condition  of  the  animal. 
We  find  at  the  same  time  many  reaction  movements  of  a  fixed  character, 
dependent  largely  on  the  structure  of  the  organism,  as  we  do  in  bacteria 
and  infusoria.  Many  of  these  specific  responses  to  specific  stimuli 
are  so  definitely  adapted  to  the  precise  conditions  under  which  the 
organism  lives  that  we  can  hardly  resist  the  conclusion  that  they  have 
been  developed  in  some  way  under  the  influence  of  these  conditions, 
as  a  result  of  the  fact  that  they  are  beneficial  to  the  organism.  Such,  for 
example,  is  the  quick  though  complicated  grasping  and  feeding  reaction 
by  which  Gonionemus  responds  to  a  moving  object.  Possibly  such 
determinate  reactions  have  arisen  through  fixation  of  movements  which 
were  originally  reached  by  a  process  of  trial,  —  a  possibility  to  which 
we  shall  return  in  our  general  analysis  of  behavior. 

In  the  Ccelenterata  we  find  also,  as  in  Amoeba,  a  certain  number  of 


BEHAVIOR   OF   CCELENTERATA  231 

responses  due  to  the  simple,  direct  reaction  (by  contraction)  of  the  part 
affected  by  a  local  stimulus.  Where  such  simple  and  perhaps  primi- 
tive reactions  are  advantageous  to  the  organism,  they  are  preserved  as 
important  factors  in  behavior,  as  in  the  negative  reactions  of  medusae. 
Where  they  are  not  advantageous  to  the  organism,  they  are  replaced, 
supplemented,  or  followed  by  more  complicated  reactions,  so  that  they 
form  a  comparatively  unimportant  feature  in  the  behavior  of  most  of 
these  animals. 

In  ccelenterates  we  find  the  same  dependence  of  behavior  on  the 
physiological  state  of  the  organism  that  we  found  so  marked  in  Pro- 
tozoa. The  same  organism  does  not  react  always  in  the  same  way  to 
the  same  external  conditions.  In  the  present  group  the  dependence  of 
behavior  on  the  progress  of  the  internal  physiological  processes,  par- 
ticularly those  of  metabolism,  stands  out  strongly.  The  animal  in  which 
material  for  the  metabolic  processes  is  abundant  differs  radically  in  its 
behavior  from  the  hungry  specimen.  The  reaction  to  a  given  stimulus 
depends  not  alone  on  the  anatomical  structure  of  the  animal  and  the 
nature  of  the  stimulus,  but  also  upon  the  way  the  internal  processes 
are  taking  place.  We  cannot  predict  how  an  animal  will  react  to  a 
given  condition  unless  we  know  the  state  of  its  internal  physiological 
processes,  and  often  whether  a  positive  or  negative  reaction  will  help 
or  hinder  the  normal  course  of  these  processes.  The  external  processes 
of  behavior  are  an  outgrowth  and  continuation  of  the  internal  processes. 

The  state  of  the  organism  as  regards  its  metabolic  processes  seems 
indeed  the  most  important  determining  factor  in  its  behavior.  Certain 
internal  metabolic  states  drive  the  animal,  without  the  action  of  any 
external  agent,  to  the  performance  of  long  trains  of  activity,  of  exactly 
the  same  character  as  may  also  be  induced  by  external  stimulation. 
The  state  of  the  metabolic  processes  likewise  determines  the  general 
nature  and  the  details  of  the  reactions  to  external  stimuli.  It  decides 
whether  Hydra  shall  creep  upward  to  the  surface  and  toward  the  light, 
or  shall  sink  to  the  bottom ;  how  it  shall  react  to  chemicals  and  to  solid 
objects;  whether  it  shall  remain  quiet  in  a  certain  position,  or  shall 
reverse  this  position  and  undertake  a  laborious  tour  of  exploration.  It 
decides  whether  the  sea  anemone  shall  react  to  indifferent  bodies,  and 
to  food,  by  the  long  and  complex  "food  reaction"  or  the  equally  long 
and  complex  "rejecting  reaction."  It  determines  whether  Cerianthus 
shall  remain  quietly  in  its  tube  in  the  sand,  or  shall  seek  a  new  abode. 
Innumerable  details  of  behavior  are  determined  in  the  ccelenterates 
by  this  factor. 

The  same  dependence  of  behavior  on  the  metabolic  processes  of  the 
organism  we  have  seen  in  the  Protozoa,  and  especially  in  the  bacteria. 


232  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

Here,  however,  the  change  of  behavior  of  a  given  individual  with  a 
change  in  these  processes  needs  further  investigation ;  this  has  been 
experimentally  demonstrated  only  with  reference  to  respiratory  pro- 
cesses in  certain  green  organisms.  In  higher  animals  the  dependence 
of  the  behavior  on  the  state  of  metabolism  is  of  course  most  evident. 

This  dependence  of  the  reaction  to  stimuli  on  the  relation  of  external 
conditions  to  internal  processes  is  a  fact  of  capital  importance,  which 
may  furnish  us  a  key  to  many  phenomena  that  are  obscure  from  other 
standpoints.  The  processes  of  metabolism  are  not  the  only  ones  occur- 
ring in  organisms,  and  the  relation  of  external  conditions  to  other 
internal  processes  may  equally  determine  behavior.  This  is  perhaps 
the  most  fundamental  principle  for  the  understanding  of  the  behavior 
of  organisms. 

Of  a  character  differing  from  those  just  considered  are  certain 
other  factors  which  modify  behavior  in  the  ccelenterates.  Past  stimuli 
received  and  past  reactions  given  are,  as  in  the  Protozoa,  important 
determining  factors  in  present  behavior;  they  may  cause  either  the 
cessation  of  reaction  to  a  given  stimulus,  or  a  complete  change  in  the 
character  of  the  reaction.  Certain  simple  conditions  produce  a  ten- 
dency in  the  organism  to  perform  more  readily  an  act  previously  performed 
(p.  206).  The  internal  state  of  the  organism  may  be  changed  in  most 
varied  ways,  giving  rise  to  corresponding  changes  in  behavior.  These 
facts  give  behavior  great  complexity,  as  well  as  great  regulative  value* 
even  in  so  low  a  group  as  the  one  now  under  consideration. 

LITERATURE    XI 

Behavior  of  Ccelenterata 

A.  Behavior  of  Hydra:  Wagxer,  1905;  Wilson,  1891 ;  Marshall,  1882; 
Pearl,  1901  ;  Mast,  1903;  Tremblev,  1744. 

B.  Behavior  of  sea  anemones:  Loeb,  1891,  1895,  1900;  Nagel,  1892,  1894, 
1894  «;   Parker,  1896,  1905,  1905  a;  Torrev,  1904;  Jennings,  1905  a;  Alla- 

BACH,  I905;    CARLGREN,  I905  ;    BURGER,   I905. 

C.  Behavior  of  hydroids  :  Torrey,  1904  a. 

D.  Behavior  of  jellyfish  :  Romanes,  1885;  Yerkes,  1902  a,  1902  b,  1903, 
1904;  Perkins,  1903;  Bancroft,  1904;  Loeb,  1900,  1900  a. 


CHAPTER  XII 

GENERAL   FEATURES   OF   BEHAVIOR   IN   OTHER   LOWER 

METAZOA 

The  foregoing  chapters  attempt  to  give  a  connected  systematic 
account  of  behavior  in  the  Protozoa  and  the  Ccelenterata.  These 
may  serve  as  types  of  the  lower  organisms.  The  necessary  spatial 
limits  of  the  present  work  render  impossible  a  similar  treatment  of 
other  groups.  We  must  content  ourselves  therefore  with  a  survey  of 
some  of  the  main  features  of  behavior  in  some  other  invertebrates. 
We  shall  take  into  consideration  chiefly  the  lower  groups. 

i.   Definite   Reaction   Forms    ("Reflexes") 

In  the  action  systems  of  most  organisms  we  find  certain  well-defined 
reaction  forms,  or  what  are  often  known  as  reflexes,1  which  make  up  a 
large  proportion  of  the  behavior.  In  the  groups  we  have  thus  far  con- 
sidered, such  definite  reaction  types  are  seen  in  the  avoiding  reactions 
of  infusoria,  the  definite  contractions  occurring  in  response  to  stimuli 
in  the  Protozoa  and  Ccelenterata,  the  bending  of  the  tentacles  toward 
the  mouth  when  stimulated  by  food,  in  the  hydroids  and  sea  anemones, 
and  in  many  other  features  of  the  behavior.  It  is  true,  as  we  have 
seen,  that  even  these  so-called  reflexes  are  usually  variable  when  studied 
in  detail,  and  their  occurrence  and  combination  depend  upon  a  mul- 
tiplicity of  internal  as  well  as  external  conditions.  Yet  certain  elements 
of  behavior  do  occur  in  accordance  with  a  definite  type,  and  this  fact 
is  one  of  much  importance.  In  some  lower  animals  behavior  is  largely 
made  up  of  such  definite  reaction  forms.  This  fact  has  assumed  an 
overshadowing  importance  in  much  recent  work  on  behavior;  investi- 
gation has  taken  largely  the  form  of  a  search  for  precisely  definable 
reflexes  and  tropisms,  and  for  conditions  under  which  they  occur  in  the 
typical  way,  while  other  factors  in  the  behavior  have  been  neglected. 
Since  these  matters  have  been  so  much  dwelt  upon,  we  need  not  take 
them  up  in  great  detail  in  the  present  work. 

The  best-known  case  of  behavior  made  up  largely  of  such  definite 

1  The  use  of  this  term  will  be  discussed  later. 
233 


234  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

reaction  forms  is  that  of  the  sea  urchin,  as  studied  by  v.  Uexkiill  (1897, 
1897a,  1899,  1900,  1900a).  The  sea  urchin  differs  from  most  lower 
animals  in  bearing  large  numbers  of  motor  organs 
scattered  over  its  entire  surface.  Most  prominent  of 
these  are  the  spines,  which  are  movable,  and  may  be 
used  as  legs,  or  as  means  of  defence.  Among  the 
spines  are  certain  peculiar  jawlike  organs  known  as 
pedicellariae  (Fig.  133),  each  borne  on  a  movable  stalk. 
These  jaws  frequently  open  and  close,  seizing  foreign 
objects.  The  surface  of  the  body  between  the  spines 
and  pedicellariae  is  covered  with  cilia.  Finally,  the 
body  bears  five  double  rows  of  tube  feet,  — -  fleshy 
tubular  suckers,  protruded  through  rows  of  holes  in 
the  shell.  These  are  important  organs  of  prehension 
Fig.  133.  — One      ^    locomotion.      All  these    different   sets   of    organs 

of    the    pedicellariae  _  ° 

from  a  sea  urchin,  are  interconnected  by  a  network  of  nerves,  one  set 
After  v.  Uexkiill.  iying  on  the  outer  surface  of  the  shell,  another  on  the 
inner  surface.  These  nerves  connect  with  the  five  radial  nerve  trunks, 
which  unite  to  form  a  ring  surrounding  the  mouth. 

V.  Uexkiill  finds  that  each  of  these  organs  (omitting  the  cilia)  has 
a  number  of  definite  reactions  or  reflexes,  which  it  performs  in  response 
to  definite  stimuli.  In  these  reactions  each  organ  may  act  as  an  inde- 
pendent individual.  If  a  piece  of  the  shell  bearing  but  a  single  spine  or 
pedicellaria  is  removed,  this  organ  reacts  to  external  stimuli  in  essen- 
tially the  same  way  as  when  connected  with  the  entire  animal.  These 
reflexes  change  with  different  intensities  and  qualities  of  stimuli,  and 
with  certain  other  conditions,  and  they  are  different  in  diverse  sorts  of 
pedicellariae.  But  each  reflex  has  a  very  definite  character.  Thus  the 
sea  urchin  appears  to  be  made  up  of  a  colony  of  almost  independent 
structures.  Each  of  these  structures  has  reactions  of  such  a  character 
that  they  perform  certain  functions  that  are  useful  in  the  life  economy 
of  the  animal. 

Yet  these  organs  are  not  entirely  independent.  They  are  connected 
by  the  nervous  network  in  certain  definite  ways,  so  that  when  one  of 
them  performs  a  certain  action,  others  may  receive  a  transmitted  stimu- 
lus, and  may  perform  the  same  or  a  differing  action.  That  is,  each 
organ  may  receive  stimuli  not  only  from  the  outer  world,  but  also, 
through  the  nerves,  from  other  parts  of  the  body.  These  interconnec- 
tions are  of  such  a  character  that  they  cause  the  various  organs  to  work 
in  harmony,  usually  assisting  to  perform  certain  necessary  functions. 

Thus,  if  debris  falls  upon  the  sea  urchin,  the  pedicellariae  seize  it, 
break  it  into  bits,  and  with  the  aid  of  the  spines  and  the  cilia  remove 


BEHAVIOR   IN  LOWER  METAZOA  235 

it  from  the  body.  Small  animals  coming  in  contact  with  the  sea  urchin 
are  seized  by  the  pedicellariae  and  held,  till  they  are  grasped  by  the  slow- 
moving  tube  feet  and  spines,  and  by  them  carried  to  the  mouth  and  eaten. 
When  the  sea  urchin  is  attacked  by  an  enemy,  the  spines  all  bend 
toward  the  region  of  attack,  presenting  a  serried  array  of  sharp  points  to 
the  advancing  enemy.  In  some  species  this  occurs  even  when  a  shadow 
falls  upon  the  animal.  The  spines  present  their  points  to  the  shaded 
side,  thus  arranging  for  an  effective  defence  in  case  the  animal  which 
has  cast  the  shadow  shall  advance  to  an  attack.  In  some  sea  urchins, 
poisonous  pedicellariae  seize  an  enemy,  usually  causing  a  quick  retreat. 
Further,  when  the  animal  is  severely  stimulated  from  one  side,  the 
reflexes  of  the  spines  are  so  arranged  as  to  carry  the  animal  in  the  op- 
posite direction.  When  attacked,  the  animal  is  thus  effectively  defended, 
while  at  the  same  time  it  flees. 

V.  Uexkiill  emphasizes  the  independence  of  these  organs,  the  defi- 
nite character  of  their  reflexes,  and  the  definiteness  of  the  interconnections 
between  them.  These  qualities  give  the  characteristic  stamp  to  the 
behavior  of  the  sea  urchin.  According  to  v.  Uexkiill,  this  animal  is 
a  "republic  of  reflexes."  Every  reflex  is  of  the  same  rank,  and  is  in- 
dependent of  the  others,  save  for  the  definite  connections  that  we  have 
mentioned.  There  is  nothing  like  a  central  unity  controlling  the  re- 
flexes, according  to  v.  Uexkiill.  The  sea  urchin,  he  holds,  is  a  bundle 
of  independent  organs,  and  it  is  only  through  the  arrangement  of  these 
organs  that  a  seemingly  unified  action  is  produced.  "It  is  only  by  the 
synchronous  course  of  the  different  reflexes  that  there  is  simulated  a 
unified  action,  which  really  does  not  exist.  It  is  not  that  the  action  is 
unified,  but  the  movements  are  ordered,  i.e.  the  course  of  the  different 
reflexes  is  not  the  result  of  a  common  impulse,  but  the  separate  reflex 
arcs  are  so  constituted  and  so  put  together  that  the  simultaneous  but 
independent  course  of  the  reflexes  in  response  to  an  outer  stimulus 
produces  a  definite  general  action,  just  as  in  animals  in  which  a  common 
centre  produces  the  action"  (1899,  p.  390).  The  difference  between 
the  behavior  of  the  sea  urchin  and  that  of  higher  animals  is  concretely 
expressed  by  v.  Uexkiill  in  the  statement  that  when  a  dog  runs  the 
animal  moves  its  legs ;  when  the  sea  urchin  runs  the  legs  (spines)  move 
the  animal. 

Yet  the  fixity  of  these  reactions  is  by  no  means  absolute,  even  in  the 
sea  urchin.  As  we  shall  see  in  the  next  section,  v.  Uexkiill  discovered 
a  number  of  definite  laws  in  accordance  with  which  they  change,  and 
there  is  positive  evidence  of  still  other  modifying  factors  not  easily 
formulated. 

In  scarcely  any  other  group  of  lower  animals  does  there  appear  to 


236  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

be  such  a  multiplicity  of  these  definite  units  of  reaction  as  in  the  sea 
urchin.  In  the  starfish  the  extension  and  withdrawal  of  the  tube  feet, 
and  the  extrusion  and  withdrawal  of  the  stomach  in  feeding,  may  be 
considered  examples.  In  free-swimming  rotifers  we  find  an  avoiding  re- 
action similar  in  all  essentials  to  that  of  the  ciliate  infusoria,  the  animals 
when  stimulated  turning  toward  a  structurally  defined  side.  There 
is  the  same  variability  in  this  reaction  that  we  find  in  the  infusoria.  In 
planarians,  the  earthworm,  and  many  other  worms,  reactions  of  a  fairly 
well-defined  character  are  seen  in  the  turning  of  the  head  toward  certain 
stimuli  and  away  from  others.  These  reactions  play  a  large  part  in 
the  behavior  of  Planaria,  according  to  Pearl  (1903).  Weak  stimuli  of 
all  sorts  affecting  one  side  of  the  body  cause  the  positive  turning ;  stronger 
ones,  the  negative  turning. 

Such  reactions  often  depend  closely  on  the  localization  of  the  stimu- 
lus. This  may  be  illustrated  from  the  behavior  of  the  flatworm  just 
mentioned.  A  weak  stimulus  at  the  side  of  the  head,  near  the  anterior 
tip,  causes  the  head  to  turn  only  a  little  toward  the  side  touched.  If 
the  stimulus  is  farther  back,  the  turning  is  greater.  In  each  case  the 
turning  is  so  regulated  with  reference  to  the  point  stimulated  as  to  direct 
the  animal  very  accurately  toward  the  region  from  which  the  stimulus 
came ;  this  aids  it  much  in  finding  food.  If  something  touches  the  flat- 
worm  lightly  at  the  middle  of  the  upper  surface  of  the  head,  the  reaction 
is  much  modified.  The  head  is  sharply  raised  and  twisted,  so  as  to 
direct  the  anterior  tip  toward  the  stimulating  object,  and  in  such  a  way 
that  the  ventral  surface  will  first  come  in  contact  with  this  object  as  the 
animal  moves  forward.  Similar  regulatory  changes  occur  in  the  nega- 
tive reaction.  A  strong  stimulus  at  the  side  of  the  anterior  end  causes 
a  quick  turning  away.  A  similar  stimulus  at  one  side  behind  the  middle 
causes  no  turning  away,  but  only  a  movement  forward.  At  intermedi- 
ate regions  there  is  a  combination  of  the  two  reactions,  the  animal  glid- 
ing forward  and  at  the  same  time  turning  away.  The  farther  back  the 
stimulus  is  given  the  greater  is  the  tendency  to  react  by  moving  forward 
in  place  of  turning  away.  This  change  of  reaction  with  a  change  in 
the  point  stimulated  is  of  course  regulatory.  An  intense  stimulus  at 
the  anterior  end  is  best  avoided  by  turning  away,  while  one  near  the 
posterior  end  is  most  easily  escaped  by  moving  rapidly  forward. 

In  most  animals  there  are  found  a  certain  number  of  these  relatively 
fixed  reaction  types  which  are  determined  by  the  usual  conditions  of 
existence,  —  gravity,  light,  temperature  changes,  contact  with  solids, 
etc.  We  have  examined  a  considerable  number  of  these  in  the  Protozoa 
and  Ccelenterata.  In  such  reactions  the  organism  often  turns  or  bends 
directly  toward  or  away  from  the  source  of  stimulation,  as  in  the  posi- 


BEHAVIOR  IN   LOWER  METAZOA  237 

tive  and  negative  reactions  of  the  flatworm.  Reactions  of  this  charac- 
ter are  commonly  spoken  of  as  tropisms.  In  the  higher  animals  and 
man  behavior  is,  of  course,  largely  determined  by  the  same  factors.  As 
we  have  seen  in  previous  chapters  and  shall  find  in  the  following  sec- 
tions of  the  present  one,  in  neither  lower  nor  higher  animals  are  the 
reactions  with  reference  to  the  general  forces  of  nature  of  a  completely 
fixed  and  invariable  character.1 

In  more  complex  animals  than  those  considered  in  the  present  vol- 
ume, definite  reaction  forms  are  often  combined  into  complex  trains  of 
action  which  are  known  as  instincts.  Recent  work  has  shown  that  in 
these  instincts  there  is  by  no  means  that  absolute  fixity  of  behavior  that 
was  formerly  assumed  to  exist.  A  detailed  treatment  of  this  matter 
would  take  us  outside  the  field  of  the  present  work. 

In  the  highest  animals  and  man,  definite  reaction  forms,  which  may 
take  place  in  certain  organs  independently  of  the  rest  of  the  body,  are 
of  course  found  as  abundantly  as  in  lower  organisms.  Such  reactions 
are  seen  in  the  reflexes  of  muscles,  etc.,  which  persist  even  after  the 
muscle  has  been  removed  from  the  body.  There  is  no  difference  in 
principle  along  this  line  between  higher  and  lower  animals.  The 
former  possess  a  much  larger  number  of  such  definite  types  of  move- 
ment, and  these  doubtless  make  up  fully  as  large  a  portion  of  behavior 
as  in  the  lower  animals. 

There  are  some  accounts  of  behavior  in  various  lower  animals  in 
wrhich  only  these  definite  reaction  forms  are  described  and  only  those 
conditions  are  dealt  with  in  which  these  appear  in  the  typical  way. 
Such  accounts  have  given  rise  to  a  widespread  impression  that  behavior 
in  the  lower  animals  differs  from  that  of  higher  forms  in  that  it  is  of  a 
fixed,  stereotyped  character,  occurring  invariably  in  the  same  way  under 
the  same  external  conditions.  This  impression  is  in  a  high  degree 
erroneous.  These  definable  reaction  forms  are  usually  in  themselves 
variable  within  wide  limits,  as  exemplified  in  the  avoiding  reaction  of 
infusoria.  But  even  if  this  were  not  true,  the  criteria  for  judging  as  to 
the  fixity  or  modifiability  of  behavior  are  to  be  derived  from  the  study 
of  the  conditions  that  induce  reaction,  that  determine  which  of  several 
possible  reactions  shall  occur,  and  that  determine  the  order  and  combina- 
tion of  reactions.  Such  a  study  shows  that  in  lower  as  well  as  in  higher 
animals  varied  internal  conditions  and  changes  are  of  the  greatest  im- 
portance in  determining  behavior,  the  animal  by  no  means  behaving 
always  in  the  same  way  under  the  same  external  conditions.  With  this 
aspect  of  the  matter  we  shall  deal  in  the  two  following  sections. 

1  See,  for  example,  the  section  on  reactions  to  gravity  in  ccelenterates,  Chapter  XI. 


238  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

2.     Reaction  by  Varied  Movements,  with  Selection  from  the 

Resulting  Conditions 

In  the  foregoing  section  we  have  dealt  with  the  fact  that  stimulation 
often  causes  the  performance  of  actions  that  are  of  a  definite,  typical 
character,  such  as  are  often  called  reflexes.  But  this  by  no  means  ex- 
hausts the  problem  of  behavior,  as  our  account  of  the  matter  in  unicel- 
lular animals  and  in  Ccelenterata  has  shown  us.  Indeed,  we  find  it  not 
to  be  the  rule  that  an  animal  when  stimulated  performs  a  single  definite 
movement,  then  returns  to  its  original  state.  On  the  contrary,  stimula- 
tion is  usually  followed  by  varied  movements,  and  the  animal  may  con- 
tinue active  long  after  the  external  agent  has  ceased  to  impinge  upon  it. 
The  continued  varied  movements  subject  the  organism  successively  to 
many  different  conditions,  external  and  internal.  In  one  of  these  con- 
ditions the  animal  remains  through  a  cessation  of  the  changes  in  activ- 
ity. It  may  thus  be  said  to  select  certain  conditions  through  the  pro- 
duction under  stimulation  of  varied  movements.  We  have  seen  many 
examples  of  this  type  of  behavior  in  the  groups  thus  far  considered. 

Behavior  of  this  character  is  very  general  in  lower  animals.  We 
shall  in  the  present  section  give  a  number  of  examples,  taken  from 
diverse  classes  of  invertebrates. 

As  we  have  seen,  the  echinoderms  furnish  perhaps  the  best  examples 
of  organisms  in  which  the  behavior  is  made  up  largely  of  more  or  less 
independent  "reflexes."  Yet  in  the  same  group  we  find  that  much  of 
the  behavior  is  of  the  type  now  under  consideration.  There  is,  of  course, 
no  opposition  between  the  two,  the  different  "reflexes"  forming  the 
variables  out  of  which  behavior  of  the  present  sort  is  made  up.  The 
pedicellarke  of  the  sea  urchin  have,  as  we  have  seen,  a  number  of  these 
definite  reflexes.  When  the  entire  animal  is  suddenly  and  strongly 
stimulated,  by  mechanical  shock,  by  a  chemical,  or  by  light,  the  pedi- 
cellariae respond,  not  by  a  single  definite  reflex,  but  by  beginning  to 
move  about  in  all  directions  (v.  Uexkiill).  They  seem  to  feel  and 
scrape  the  entire  surface  of  the  body,  seizing  anything  with  which  they 
come  in  contact,  and  this  behavior  may  continue  for  an  hour  or  more 
after  stimulation  has  ceased.  Similar  effects  are  often  produced  in  the 
spines  by  a  general  stimulus.  They  wave  about,  their  tips  describing 
circles,  and  this  may  continue  for  a  long  time.  Such  reactions  are  seen 
also  in  the  tube  feet.  When  the  sea  urchin  or  starfish  is  suspended  in 
the  water  or  is  placed  on  its  back,  the  tube  feet  extend  and  wave  back 
and  forth,  as  if  searching  for  something  to  which  they  might  attach 
themselves. 

On  a  more  extensive  scale,  the  "righting"  reaction  of  the  starfish  is 


BEHAVIOR   IN   LOWER    METAZOA  239 

a  notable  example  of  behavior  that  is  not  stereotyped,  but  is  flexible  and 
variable.  The  usual  course  of  this  reaction  is  as  follows:  After  the 
starfish  has  been  placed  on  its  back,  it  extends  its  tube  feet  and  moves 
them  about  in  all  directions.  At  the  same  time  the  tips  of  the  arms  be- 
come twisted,  so  that  some  of  the  tube  feet  are  directed  downward.  In 
this  way,  after  a  time,  some  of  the  feet  become  attached  to  the  bottom. 
These  begin  to  pull  on  the  arm  to  which  they  belong,  turning  it  farther 
over  and  bringing  other  tube  feet  into  contact  with  the  bottom;  these 
now  assist  in  the  process.  If  two  or  three  adjacent  rays  become  thus 
attached,  the  other  rays  cease  their  searching,  twisting  movements,  and 
allow  themselves  to  be  turned  over  by  the  activities  of  the  tube  feet  of 
the  attached  rays.  If  two  or  more  opposite  rays  become  attached  to 
the  bottom  in  such  a  way  that  they  oppose  each  other,  then  one  releases 
its  hold,  and  allows  the  turning  to  be  accomplished  by  the  opposing  rays. 
It  is  evident  that  the  reaction  is  an  example  of  the  performance  of  varied 
movements  under  stimulation,  with  selection  from  the  conditions  re- 
sulting; from  these  movements.  Certain  features  in  this  reaction  are  of 
special  interest.  At  first  all  the  tube  feet  and  rays  try  to  find  an  attach- 
ment. When  certain  ones  have  succeeded,  this  is  in  some  way  recog- 
nized by  those  parts  whose  action  would  oppose  the  movement,  for  these 
cease  their  attempts,  or  even  release  the  hold  already  attained.  In  some 
way  the  physiological  state  corresponding  to  "success"  in  certain  rays 
is  transmitted  to  the  other  rays,  and  they  change  their  behavior  accord- 
ingly. 

Variability  and  flexibility  are  the  essence  of  such  behavior.  This 
is  well  illustrated  by  study  of  repetitions  of  the  righting  reaction  in  the 
starfish.  It  is  by  no  means  always  the  same  arm  or  combination  of 
arms  that  initiates  and  finally  brings  about  the  turning.  The  essential 
point  is  to  get  started  in  some  way,  then  to  continue  on  the  basis  of  the 
start  made.  Preyer  (1886)  studied  this  behavior  in  the  starfish  with 
great  care.  He  says :  "  Neither  in  one  [species]  nor  the  other  is  the  method 
of  turning  always  the  same.  I  have  likewise  seen  Aster ias  glacialis, 
which  was  several  times  in  succession  turned  on  its  back  without  change 
in  the  outer  conditions,  right  itself  sometimes  in  one  manner,  sometimes 
in  another.  The  spirals  of  the  twisted  arms  do  not  work  each  time  in 
corresponding  directions,  but  at  first  the  neighboring  arms  often  oppose 
each  other.  But  soon  the  correction  takes  place,  in  that  the  attached 
feet  stop  those  that  are  disturbing  the  turning,  and  the  wrongly  twisted 
radii  straighten  out  again.  .  .  .  The  variability  of  form  in  starfish 
that  are  righting  themselves  is  great,  and  no  species  rights  itself  in  only 
one  way.  .  .  .  But  here,  too,  it  is  true  that  no  Astropecten  rights  itself 
twice  in  succession  in  exactly  the  same  way.     An  adaptation  to  the  sur- 


240  BEHAVIOR   OF   THE  LOWER  ORGANISMS 

face  of  attachment  always  occurs,  and  according  as  this  is  convex,  con- 
cave, smooth,  rough,  or  inclined,  is  the  turning  process  made  easier  or 
more  difficult,  and  brought  about  in  this  manner  or  that"  (1886,  pp.  107- 
108).  Sometimes  the  animal  turns  a  somersault;  sometimes  it  extends 
all  its  arms  upward,  taking  the  "tulip"  form  and  toppling  over  on  one 
side  —  and  so  on  through  many  variations. 

Even  the  main  features  of  the  typical  reaction  may  be  omitted  or 
changed,  the  turning  taking  place  by  means  quite  different  from  the 
usual  ones.  Thus,  Astro pecten  aiirantiacus  usually  rights  itself  by 
means  of  its  tube  feet,  but  sometimes  turns  without  using  the  tube  feet 
at  all.  Lying  on  its  back,  it  lifts  the  central  disk  high,  resting  on  the 
tips  of  three  or  four  of  the  arms.  Then  it  turns  two  of  the  arms  under, 
while  lifting  the  others  upward,  so  that  it  now  falls  with  ventral  side 
down.  During  this  action  the  tube  feet  are  moved  about  in  a  lively 
way,  and  when  the  turning  is  nearly  completed  the  tube  feet  of  the 
upper  radii  which  are  approaching  the  substratum  are  pushed  far  out, 
as  if  preparatory  to  meeting  the  bottom. 

When  a  portion  of  the  feet  were  prevented  from  acting,  by  subjecting 
them  to  alcohol  or  other  drugs,  Preyer  found  that  the  starfish  righted 
itself  by  means  of  the  remaining  ones,  and  by  bending  and  twisting  its 
arms.  Pieces  of  the  arms  may  right  themselves,  and  this  again  occurs 
in  many  different  ways. 

The  thorough  study  of  the  movements  and  reactions  of  the  starfish 
made  by  Preyer  (1886)  shows  that  the  righting  reaction  is  typical  of  the 
entire  behavior.  If  the  starfish  is  suspended  just  below  the  surface  of 
the  water  with  ventral  side  up,  by  threads  attached  to  the  tips  of  its 
arms,  it  performs  varied  movements,  until  in  the  course  of  time  it  turns 
over,  just  as  in  the  usual  righting  reaction.  If  a  short  rubber  tube  was 
slipped  over  one  of  the  arms  of  a  brittle  star,  to  its  base,  Preyer  found 
that  this  caused  the  animal  to  perform  many  varied  movements,  till  by 
one  of  them  the  tube  was  removed.  Sometimes  the  animal  merely 
moved  rapidly  forward,  dragging  the  arm  bearing  the  tube  behind  it 
till  the  tube  was  scraped  off.  Sometimes  the  animal  placed  one  or  two 
of  the  other  arms  against  the  tube  and  forced  it  off.  In  other  cases  the 
covered  arm  was  dropped  from  the  body  (as  often  happens  in  brittle 
stars).  Again,  sometimes  the  arm  bearing  the  tube  was  lifted  and 
waved  back  and  forth,  till  the  tube  was  in  this  way  displaced.  Thus 
Preyer  observed  five  different  ways  in  which  the  tube  was  finally  re- 
moved; as  he  remarks,  "If  one  method  does  not  help,  another  is  used." 
It  may,  of  course,  be  maintained  that  in  all  these  cases  the  removal  of 
the  tube  was  in  a  sense  accidental.  But  this  is  precisely  the  essential 
point  in  much  of  the  behavior  of  lower  organisms.     When  stimulated 


BEHAVIOR   IN   LOWER   METAZOA  241 

they  perform  varied  movements,  till  one  of  these  "accidentally"  re- 
moves the  source  of  stimulation.  How  this  may  develop  into  more 
directly  regulatory  reactions  we  shall  consider  in  the  next  section. 

The  same  qualities  are  shown  in  certain  experiments  of  Preyer  in 
which  he  attempted  to  confine  the  starfish  by  means  of  large,  flat-headed 
pins.  These  were  placed  in  the  angles  between  the  rays,  close  against 
the  disk,  and  driven  into  the  board  on  which  the  starfish  lay.  They 
thus  held  it  down  without  injury.  The  starfish  in  the  course  of  time 
escapes  from  the  pins,  but  only  after  much  effort.  The  animals  try 
successively  various  methods, "  now  they  seek  to  force  themselves  through, 
now  to  climb  over  the  top,  now  to  push  through  by  turning  on  one  side." 
In  scarcely  any  two  cases  does  the  process  of  escape  occur  in  the  same 
way,  according  to  Preyer.  The  behavior  is  as  far  as  possible  from  that 
of  invariable  reflexes  always  occurring  in  the  same  way  under  the  same 
external  conditions. 

One  further  point  mentioned  by  Preyer  is  of  great  interest.  He  says 
that  when  the  experiment  is  repeated  with  the  same  individual,  the 
time  required  for  escape  becomes  less.  The  number  of  useless  move- 
ments, "superfluous  twistings,  feelings  about,  and  forward  and  back- 
ward motions,"  becomes  less  the  oftener  the  individual  has  been  placed 
in  such  a  situation.  If  this  is  true,  we  have  in  so  low  an  animal  as  the 
starfish  regulation  through  the  selection  of  conditions  produced  by 
varied  movements  passing  into  a  more  directly  regulatory  action;  in 
other  words,  what  is  commonly  called  in  higher  animals  intelligence. 
There  seems  to  be  no  reason  for  doubting  Preyer's  observations  on  this 
point,  but  on  account  of  their  great  importance  they  should  be  repeated 
and  verified  or  refuted. 

Many  other  illustrations  of  behavior  of  the  general  character  set 
forth  above  could  be  presented  from  the  valuable  work  of  Preyer  (1886). 
It  has  become  the  fashion  to  neglect  and  even  speak  slightingly  of  the 
work  of  Preyer  on  the  behavior  of  the  starfish.  This  seems  to  be  due 
to  the  tendency  observable  in  recent  scientific  literature  to  represent  all 
such  matters  as  extremely  simple  and  reducible  to  separate  well-known 
mechanical  factors,  and  to  avoid  all  experiments  tending  to  reveal  the 
fallacy  of  this  view.  Preyer  was  not  afraid  to  open  his  eyes  by  properly 
designed  analytical  experiments  to  the  complexity  and  regulatory  charac- 
ter of  the  behavior.  Such  thorough  and  detailed  studies  of  animal  be- 
havior as  that  of  Preyer  on  the  starfish  are  rare  at  the  present  time ;  his 
work  stands  in  this  respect  in  most  refreshing  contrast  with  some  of  the 
superficial  work  recently  put  forth.  The  excellent  work  of  Romanes 
(1885)  had  already,  before  Preyer,  brought  out  many  examples  of  the 
style  of  behavior  we  have  illustrated  above. 


242 


BEHAVIOR  OF   THE  LOWER  ORGANISMS 


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In  many  free-swimming  Rotifera  the  chief  methods  of  movement  and 
reaction  are  similar  even  in  details  to  those  of  the  free-swimming  infusoria, 
which  we  have  already  described.  Like  the  infusoria, 
these  rotifers  swim  by  means  of  cilia,  revolve  on  the 
long  axis,  and  swerve  toward  one  side  (usually  dor- 
sal), as  they  progress.  The  cilia  produce  a  current 
passing  from  in  front  to  the  mouth  and  ventral  side, 
thus  allowing  the  animals  to  test  the  conditions  in 
advance.  To  most  effective  stimuli  these  rotifers 
react,  as  do  the  infusoria,  by  swerving  more  than 
usual  toward  one  side,  —  usually  the  dorsal  side. 
Thus  the  spiral  becomes  much  wider,  and  the  ani- 
mals are  pointed  successively  in  many  different  direc- 
tions and  subjected  to  many  different  conditions.  In 
time  they  may  thus  reach  conditions  which  relieve 
them  of  the  action  of  the  stimulating  agent.  There- 
upon the  reaction  ceases,  so  that  the  animals  con- 
tinue in  the  direction  which  has  thus  been  reached. 
All  the  general  features  of  the  reactions  are  essen- 
tially like  those  of  infusoria,  so  that  we  need  not 
enter  into  details.  The  reactions  to  mechanical  stim- 
uli, to  chemicals,  to  heat  and  cold,  to  light,  and  to 
electricity  are  known  to  occur  in  the  way  just 
•      'a  I34i  —  Pla"  sketched,   in   a   number  of  species.     Orientation    to 

nana,      dorsal      view.    <  r 

After  Woodworth.  light  and  to  the  electric  current  takes  place  in  the 
same  way  as  the  orientation  to  light  in  Euglena  and  Stentor.  It  is  inter- 
esting to  observe  that  in  the  Rotifera,  owing  to  the  concentration  of  the 
cilia  at  one  end  of  the  animal,  there  is  no  such  incoherence  and  lack  of 
coordination  in  the  reaction  to  the  constant  electric  current,  as  is 
found  in  infusoria.  The  rotifer  (Anurcea  cochlear  is)  becomes  oriented 
with  anterior  end  to  the  cathode  by  the  same  method  as  in  reactions 
to  light  and  other  agents. 

In  many  rotifers  the  reaction  plan  just  described  forms  only  one 
feature  of  the  activities,  so  that  the  behavior,  taken  all  together,  may  be 
exceedingly  complex.  There  is  much  opportunity  for  further  study  of 
the  reactions  of  this  group.  But  so  far  as  known,  much  of  the  behavior 
may  be  expressed  as  follows:  When  stimulated,  the  animals  perform 
continued  and  varied  movements,  the  variations  often  taking  place  in  a 
systematic  way.  These  movements  necessarily  subject  the  animals  to 
varied  conditions,  one  of  which  is  finally  selected,  through  the  fact  that 
it  removes  the  cause  of  stimulation. 

Much  of  the  behavior  of  the  flat  worm  Planaria  (Fig.  134),  as  studied 


BEHAVIOR  IN  LOWER  METAZOA 


243 


Fig.  135.  —  Side    view  of    moving    Planaria.     After 
Pearl.     A,  body;  B,  mucus;  C,  cilia;  D,  substratum. 


by  Pearl  (1903),  may  be  summed  up  under  the  same  formula  set  forth 
in  the  preceding  paragraph.  Varied  movements  which  subject  the  ani- 
mal to  many  different  conditions,  are  seen  even  in  the  unstimulated 
specimen.  As  the  flatworm  glides  along  by  means  of  its  cilia,  the  head 
is  held  upward  (Fig.  135)  and  moved  frequently  from  side  to  side,  while 
its  margins  wave  up  and 
down,  and  are  extended 
and  contracted.  The  flat- 
worm  thus  seems  to  "feel 
its  way"  with  its  head. 
Sometimes  these  feeling 
movements  become  much 
accentuated,  the  animal  almost  or  quite  stopping,  then  raising  the 
whole  anterior  part  of  the  body  and  waving  it  about  in  the  water. 
These  movements  of  course  serve  to  test  the  environment  on  each  side ; 
in  other  words,  they  subject  the  sensitive  anterior  end  to  varied  con- 
ditions. 

The  testing  movements  are  specially  marked  under  certain  condi- 
tions. When  the  active  planarian  is  about  to  come  to  rest,  it  stops  and 
moves  the  anterior  end  from  side  to  side,  touching  any  object  that  may 
be  found  in  the  neighborhood.  After  thus  thoroughly  testing  the  sur- 
roundings, the  muscles  relax  and  the  animal  comes  to  rest.  When  later 
the  animal  resumes  its  active  progression,  this  begins  again  with  the 
testing  movements  of  the  head. 

The  same  testing  movements  are  seen  under  various  sorts  of  stimu- 
lation.     On  coming  to  a  solid  body,  the  flatworm   moves  the  head 
about  over  its  surface.     If  it  turns  out  to  be  some- 
thing fit  for  food,  the  animal  now  feeds  upon  it,  other- 
wise  it    moves   away  again.   .  If    while  a  number  of 
specimens  of  Planaria  are  moving  in  a  certain  direc- 
tion, the  direction  of  the  light  is  changed  so  as  to  fall 
upon  their  anterior  ends,  they  usually  turn  the  head 
from  side  to  side  two  or  three  times,  then  follow  up 
one  of  these  movements  by  turning  the  body  till  it  is 
finally  directed  away  from  the  light.     These  testing 
movements  are  also  seen  when  the  animal  begins  to 
Fig    i  6  —  Re-  drv>  an<^  when  the  water  is  heated;  the  worm  gives  the 
action  of  Planaria  to  impression  that  it  is  seeking  about  for  other  conditions. 
drying.    After  Pearl.         Qther  features  of  the  reactions  to  drying  and  to 

temperature  changes  are  of  interest  from  our  present  standpoint.  If 
the  planarian  is  laid  on  a  glass  plate,  as  soon  as  the  tendency  to  dry 
becomes  evident  the  worm  curls  up  closely  and  thrusts  the  head  under 


244 


BEHAVIOR   OF   THE  LOWER  ORGANISMS 


the  body  (Fig.  136).  In  this  way  the  exposed  surface  of  the  body  is 
made  as  small  as  possible,  and  the  sensitive  head  especially  is  kept  from 
drying.  At  intervals  the  animal  straightens  out,  extends  its  head  as 
far  as  possible,  and  waves  it  from  side  to  side.  If  in  this  way  it  finds 
water,  it  of  course  moves  into  it.  If  it  does  not  find  water,  it  curls  up 
again.  After  a  time,  if  the  drying  becomes  more  decided,  the  animal 
attempts  to  crawl  backward.  Under  natural  conditions  drying  will 
usually  take  place  at  the  edge  of  a  pool,  and  this  backward  movement 
carries  the  animal  again  into  the  water.  All  together,  the  reaction  to 
drying  is  not  simple  and  stereotyped,  but  involves  the  successive  per- 
formance of  many  different  activities. 

In  responses  to  heat  or  cold  we  find  a  similar  train  of  activities.   If 
the  gliding  Planaria  comes  to  a  region  of  considerably  higher  or  lower 

temperature,  it  waves  its  head  back 
Zl  and  forth  several  times,  apparently 
till  it  has  determined  the  direction 
which  leads  back  to  the  usual 
temperature,  then  turns  and  moves 
in  that  direction.  Responses  of 
this  character  usually  take  place 
several  times  before  the  animal  is 
completely  directed  toward  the  re- 
gion of  optimum  temperature  (see 
Fig.  137).  If  the  temperature  of 
the  water  is  slowly  raised  in  a 
uniform  manner,  so  that  all  parts 
of  the  body  are  similarly  affected, 
then  a  series  of  reactions  occurs. 
First  the  animals  become  more 
Fig.  137.  -  -Behavior  of  the  flatworm  in  ap-  active,  gliding  about   rapidly,  ex- 

proaching  the  heated  end  of  a  trough  The  lines  tencling  the  head,  and  turning  it 
show  the  paths  followed.     At  each  of  the  points  °  ° 

marked  by  a  round  spot,  the  animal  stopped  and  toward  One  Side  Or  the  Other.       The 

waved  its  head  to  and  fro,  finally  following  up  behavior  resembles  that  of  speci- 

one  of  the  trial  movements.      I  he  figures  at  these  .  .  .       , 

points  show  the  number  of  trial  movements  that  mens  showing  the  positive  re- 
were  made,  in  each  case.     After  Mast.  actjon     to    weak    stimuli.       As     the 

temperature  rises,  the  animal  begins  to  contract  at  intervals,  and  to  turn 
the  head  frequently  and  strongly  from  side  to  side,  making  little  prog- 
ress in  advance.  The  behavior  has  now  the  characteristics  of  the 
"negative"  reaction.  As  the  temperature  rises  further,  the  turning 
ceases,  and  the  animal  begins  to  make  rapid,  violent  contractions,  such 
as  occur  in  "crawling,"  under  other  violent  stimuli.  Later  the  animal 
twists  its  body,  as  occurs  in  its  righting  reaction  when  placed  on  its 


BEHAVIOR   IN  LOWER  METAZOA 


245 


back;  it  thus  forms  a  spiral  of  two  turns.  Finally  it  behaves  in  a 
manner  somewhat  similar  to  that  shown  when  it  dries.  It  rolls  the 
two  ends  under  the  body,  arching  the  dorsal  surface.  In  this  position 
the  animal  rolls  over  on  its  back  and  dies. 

Thus  under  a  single  unlocalized  stimulus  of  gradually  increasing  in- 
tensity, the  behavior  of  the  organism  passes  through  a  series  of  stages, 
closely  resembling  the  reactions  given  under  most  diverse  conditions. 
As  Mast  (1903),  to  whom  these  observations  are  due,  expresses  it,  "the 
general  impression  is  given  that  as  the  thermal  stimulus  increases,  the 
animal  tries,  in  a  sort  of  'hit-or-miss'  way,  every  reaction  which  it  has 
at  command  in  order  to  get  rid  of  the  stimulation." 

The  "righting  reaction"  of  the  flatworm  is  another  example  of  a 
response  that  is  not  stereotyped  in  character,  but  varies  greatly.  If  the 
animal  is  turned  on  its  back,  it  quickly  rights  itself  again.  This  usually 
occurs  as  follows.     The  animal  twists  itself  into  a  spiral  (Fig.  138,  A), 


Fig.  138.  —  Righting  reactions  in  the  flatworm.  After  Pearl.  A,  reaction  of  entire  worm. 
B,  righting  reaction  of  short  piece  from  anterior  end  of  worm,  a,  b,  c,  d,  e,  /,  successive  steps  in 
the  process.  C,  righting  reaction  of  triangular  pieces,  a,  manner  in  which  the  piece  is  cut. 
b,  a  small  portion  of  the  thin  edge  turns  so  as  to  bring  the  ventral  surface  in  contact  with  the 
bottom,  c,  d,  this  turning  increases;  by  a  continuation  of  the  process  the  whole  piece  is  finally 
righted,     e,  /,  cross  sections  through  the  pieces  while  turning. 


thus  causing  the  ventral  surface  of  the  head  to  face  the  bottom,  where 
it  attaches  itself.  Then  the  worm  creeps  forward,  bringing  successively 
more  and  more  of  its  ventral  surface  in  contact  with  the  bottom,  pro- 
ceeding toward  the  rear.  Thus  the  spiral  is  unwound,  so  that  after  the 
animal  has  traversed  a  short  distance,  the  entire  ventral  surface  is  in 
contact  with  the  bottom,  as  usual. 

But  the  righting  reaction  may  take  place  in  quite  a  different  way. 
Pearl  (1903)  cut  the  planarian  into  pieces  of  such  form  that  it  could  no 


246  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

longer  twist  itself  into  a  spiral.  Then  some  portion  of  the  ventral  sur- 
face was  brought  by  other  means  into  contact  with  the  bottom,  and 
from  this  point  the  remainder  of  the  surface  was  pulled  into  contact.  In 
small  strips  from  the  head  region,  the  posterior  ends  are  turned  under, 
bringing  the  ventral  side  at  this  point  against  the  bottom,  then  by  pull- 
ing from  this  point,  the  entire  piece  was  turned  over  endwise  (Fig.  138, 
B).  In  triangular  pieces  from  the  middle  of  the  animal,  one  edge  was 
turned  under,  then  the  remainder  righted  from  this  region,  by  pulling 
the  rest  of  the  piece  over  (Fig.  138,  C).  These  modifications  bring  out 
the  essentially  adaptive  character  of  the  behavior.  The  essential  point 
seems  to  be,  to  get  some  portion  of  the  ventral  surface,  by  any  means 
whatever,  into  contact  with  the  substratum,  then  by  working  out  from 
this  point,  to  bring  the  whole  ventral  surface  into  attachment. 

From  certain  points  of  view  the  whole  behavior  of  the  flatworm  may 
be  considered  a  process  of  testing  all  sorts  of  conditions,  retaining  some 
and  rejecting  others.  As  we  have  seen  in  the  section  which  precedes 
the  present  one,  the  positive  reactions  of  this  animal  are  not  due  to  any 
specific  qualities  of  stimulation.  On  the  contrary,  the  animal  turns 
toward  weak  stimuli  of  all  sorts.  Solid  bodies,  whether  fit  for  food  or 
not,  chemicals  of  all  sorts,  including  the  injurious  as  well  as  the  bene- 
ficial, heat,  and  cold,  all  induce,  when  acting  but  slightly  on  one  side, 
a  turning  toward  the  source  of  stimulation.  The  flatworm  may  thus 
be  said  to  investigate  every  slight  change  occurring  in  its  surroundings. 
On  reaching  a  region  where  the  agent  in  question  acts  more  intensely, 
the  positive  reaction  may  either  continue  or  be  transformed  into  a  nega- 
tive one.  Thus  the  turning  toward  food  is  not  due  to  the  specific  quali- 
ties which  make  the  substance  in  question  fit  for  food,  but  is  the  result 
only  of  this  general  tendency  to  move  toward  all  sources  of  weak  stimu- 
lation. The  flatworm  proves  all  things,  holding  fast  only  to  that  which 
is  good. 

In  most  if  not  all  other  invertebrates  there  occur  many  "trial  move- 
ments" similar  to  those  already  described.  In  many  recent  accounts 
of  the  behavior  of  other  invertebrates  little  mention,  it  is  true,  will  be 
found  of  such  movements.  This  is  apparently  because  attention  has 
been  directed  by  current  theories  to  other  features  of  the  behavior,  and 
the  trial  movements  have  been  considered  of  no  consequence.  Often 
an  attentive  reading  of  papers  on  "tropisms,"  etc.,  will  reveal  paren- 
thetical mention  of  various  "disordered"  movements,  turnings  to  one 
side  and  the  other,  and  other  irregularities,  which  disturb  the  even  tenor 
of  the  "tropism,"  and  are  looked  upon  for  some  reason  as  without  sig- 
nificance and  not  requiring  explanation.  Further,  one  often  finds  in 
such  papers  accounts  of  movements  which  are  clearly  of  the  "trial" 


BEHAVIOR   IN  LOWER  METAZOA  247 

character,  yet  are  not  recognized  as  such  by  the  author,  on  the  watch 
only  for  "tropisms."  In  the  earlier  literature  of  animal  behavior,  be- 
fore the  prevalence  of  the  recent  hard-and-fast  theories,  one  finds  the 
trial  movements  fully  recognized  and  described  in  detail.  This  is  the 
case,  for  example,  in  the  classical  papers  of  Engelmann  on  behavior  in 
unicellular  organisms,  and,  as  we  have  seen  in  detail,  for  that  of  Preyer 
on  the  starfish.  Moebius,  in  1873,  gave  a  lecture  on  behavior  in  which 
examples  of  this  fact  are  found.  Thus,  he  describes  the  reaction  of  a 
large  mollusk,  Nassa,  to  chemical  stimuli,  as  shown  when  a  piece  of 
meat  is  placed  in  the  aquarium  containing  them,  in  the  following  way : 
They  do  not  orient  themselves  in  the  lines  of  diffusion  and  travel  toward 
the  meat,  but  move  "now  to  the  right,  now  to  the  left,  like  a  blind  man 
who  guides  himself  forward  by  trial  with  his  stick.  In  this  way  they 
discover  whether  they  are  coming  nearer  or  going  farther  away  from 
the  point  from  which  the  attractive  stimulus  arises"  (Moebius,  1873, 
p.  9). 

Unprejudiced  observation  of  most  invertebrates  will  show  that  they 
perform  many  movements  which  have  no  fixed  relation  to  sources  of 
external  stimuli,  but  which  do  serve  to  test  the  surroundings  and  thus 
to  guide  the  animal.  This  the  present  author  has  observed,  for  example, 
in  studies  on  the  leech,  on  various  fresh-water  annelids  and  mollusks, 
and  in  less  extended  observation  on  many  other  animals.  As  Holmes 
(1905)  has  recently  pointed  out,  in  a  most  excellent  paper,  this  is  really 
a  matter  of  common  observation  on  all  sorts  of  animals.  The  fact  that 
such  movements  are  not  emphasized  by  writers  on  animal  behavior  is 
evidently  due  to  their  being  considered  without  significance. 

In  a  number  of  recent  papers  the  importance  of  trial  movements  in 
behavior  has  been  more  explicitly  recognized.  Thus,  for  the  earthworm, 
the  recent  papers  of  Miss  Smith  (Mrs.  Philip  P.  Calvert)  (1902),  of 
Holmes  (1905),  and  of  Harper  (1905)  have  set  this  matter  in  a  clear  light. 
Miss  Smith  showed  that  in  the  reactions  of  the  earthworm  Allolobophora 
fcetida  to  heat  and  cold,  to  chemicals,  to  drying,  and  to  light,  "testing 
movements"  play  a  large  part.  When  stimulated,  the  earthworm  fre- 
quently responds  by  moving  the  head  first  in  one  direction,  then  in  an- 
other, often  repeating  these  movements  several  times.  It  then  finally 
follows  up  those  movements  which  decrease  the  stimulation.  Holmes 
(1905)  confirms  these  results,  especially  for  the  reaction  of  the  earth- 
worm to  light.  His  account  of  the  behavior  of  the  earthworm  under 
the  action  of  light  coming  from  one  side  may  be  quoted:  "It  soon  de- 
veloped that  what  seemed  at  first  a  forced  orientation,  the  result  of  a 
direct  reflex  response,  is  not  really  such,  but  that  the  orientation  which 
occurs  and  which  is  often  quite  definite  is  brought  about  in  a  more  indi- 


248  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

rect  manner  by  a  mode  of  procedure  which  is  in  some  respects  similar 
to  the  method  of  trial  and  error  followed  by  higher  forms"  (I.e.,  p.  99). 
The  precise  behavior  of  the  earthworm  in  becoming  oriented  to  light  is 
described  as  follows :  "As  the  worm  crawls  it  frequently  moves  the  head 
from  side  to  side  as  if  feeling  its  way  along.  If  a  strong  light  is  held  in 
front  of  the  worm,  it  at  first  responds  by  a  vigorous  contraction  of  the 
anterior  part  of  the  body ;  it  then  swings  the  head  from  side  to  side,  or 
draws  it  back  and  forth  several  times,  and  extends  again.  If  in  so  doing 
it  encounters  a  strong  stimulus  from  the  light  a  second  time,  it  draws  back 
and  tries  once  more.  If  it  turns  away  from  the  light  and  then  extends 
the  head,  it  may  follow  this  up  by  the  regular  movements  of  locomotion. 
As  the  worm  extends  the  head  in  crawling  it  moves  it  about  from  side  to 
side,  and  if  it  happens  to  turn  it  toward  the  light  it  usually  withdraws  it 
and  bends  in  a  different  direction.  If  it  bends  away  from  the  light  and 
extends,  movements  of  locomotion  follow  which  bring  the  animal  farther 
away  from  the  source  of  stimulus"  (I.e.,  p.  100). 

Other  observers  —  Parker  and  Arkin  (1901),  Adams  (1903) — had 
observed  that  when  the  earthworm  is  lighted  from  one  side,  it  by  no  means 
always  turns  directly  away  from  that  side ;  Adams,  however,  showed  that 
it  turns  more  frequently  away  from  the  light  than  toward  it,  thus  indicat- 
ing that  the  animal  has  some  direct  localizing  power.  This  is  confirmed 
by  Harper  (1905),  who  shows  that  in  a  strong  light  the  earthworm 
Perichseta  commonly  turns  directly  away  from  the  source  of  light, 
though  if  the  light  is  weak,  the  "trial  movements"  are  seen.  Harper 
gives  many  other  examples  of  the  performance  of  varied  movements 
under  the  action  of  stimuli  in  this  animal,  and  brings  out  some  of  the 
internal  factors  on  which  some  of  these  depend. 

Holmes  (1905)  found  that  the  leech  and  the  larva  of  the  blowfly 
react  to  light  in  essentially  the  manner  which  he  had  found  in  the  earth- 
worm. For  the  leech  the  following  account  is  given:  "In  its  progress 
the  leech  frequently  raises  the  anterior  part  of  the  body  and  waves  it 
from  side  to  side  as  if  feeling  its  way.  If  the  animal  turns  it  in  the  direc- 
tion  of  a  strong  light,  it  is  quickly  withdrawn  and  extended  again,  usu- 
ally in  another  direction.  If  the  light  is  less  strong,  it  waves  its  head 
back  and  forth  several  times  and  sets  it  down  away  from  the  light ;  then 
the  caudal  end  is  brought  forward,  the  anterior  end  extended  and  swayed 
about  and  set  down  still  farther  away  from  the  light  than  before.  When 
the  leech  becomes  negatively  oriented,  it  may  crawl  away  from  the  light, 
like  the  earthworm,  in  a  nearly  straight  line.  The  extension,  withdrawal, 
and  swaying  about  of  the  anterior  part  of  the  body  enable  the  animal  to 
locate  the  direction  of  least  stimulation,  and  when  that  is  found  it  begins 
its  regular  movements  of  locomotion.     Of  a  number  of  random  move- 


BEHAVIOR  IN   LOWER  METAZOA  249 

ments  in  all  directions  only  those  are  followed  up  which  bring  the  ani- 
mal out  of  the  undesirable  situation"  (I.e.,  p.  102). 

In  the  case  of  the  blowfly  larva,  Holmes  speaks  as  follows:  "Obser- 
vations which  I  have  made  upon  the  phototaxis  of  blowfly  larvae  with 
the  problem  of  orientation  especially  in  mind  soon  convinced  me  that 
the  movements  of  these  forms  are  directed  by  light  through  following  up 
those  random  movements  which  bring  them  away  from  the  stimulus. 
When  strong  light  is  thrown  on  a  fly  larva  from  in  front,  the  anterior  end 
of  the  creature  is  drawn  back,  turned  toward  one  side,  and  extended 
again.  Often  the  head  is  moved  back  and  forth  several  times  before  it 
is  set  down.  Then  it  may  set  the  head  down  when  it  is  turned  away  from 
the  light  and  pull  the  body  around.  If  the  head  in  moving  to  and  fro 
comes  into  strong  light,  it  is  often  retracted  and  then  extended  again  in 
some  other  direction,  or  it  may  be  swung  back  without  being  withdrawn. 
If  a  strong  light  is  thrown  upon  a  larva  from  one  side,  it  may  swing  the 
head  either  toward  or  away  from  the  light.  If  the  head  is  swung  toward 
the  light,  it  may  be  withdrawn  or  flexed  in  the  opposite  direction,  or, 
more  rarely,  moved  toward  the  light  still  more.  If  it  is  turned  away  from 
the  light,  the  larva  usually  follows  up  the  movement  by  locomotion. 
Frequently  the  larva  deviates  considerably  from  the  straight  path,  but 
as  it  continually  throws  the  anterior  part  of  the  body  about  and  most 
frequently  follows  up  the  movement  which  brings  it  away  from  the  stim- 
ulus, its  general  direction  of  locomotion  is  away  from  the  light.  In 
very  strong  illumination  the  extension  of  the  anterior  part  of  the  body 
away  from  the  light  is  followed  by  a  retraction,  since  in  whatever  direc- 
tion it  may  extend  it  receives  a  strong  stimulus  and  the  larva  writhes 
about  helplessly  for  some  time.  Sooner  or  later,  however,  it  follows  up 
the  right  movement.  Occasionally  the  larva  may  crawl  for  some  dis- 
tance directly  toward  the  light,  but  after  a  time  its  movements  carry  it 
in  the  opposite  direction.  When  once  oriented  the  direction  of  locomo- 
tion of  the  larvae  is  comparatively  straight  "  (  I.e.,  pp.  104-105). 

As  Holmes  points  out,  these  are  only  examples  of  a  very  general 
condition  of  affairs  in  the  lower  organisms.  We  cannot  do  better,  in 
concluding  this  brief  section,  than  to  quote  some  of  Holmes's  general 
remarks,  which  show  that  his  observations  have  led  him  to  essentially 
the  same  conception  of  behavior  that  we  have  reached  in  the  present 
work. 

"The  role  played  by  the  trial  and  error  method  in  the  behavior  of 
the  lower  organisms  has,  as  yet,  elicited  but  little  comment,  owing  prob- 
ably to  the  fact  that  attention  has  been  centred  more  upon  other  fea- 
tures of  their  behavior.  It  may  have  been  considered  by  some  investi- 
gators as  too  obvious  for  remark,  since  any  one  who  attentively  observes 


250  BEHAVIOR  OF   THE   LOWER   ORGANISMS 

the  conduct  of  almost  any  of  the  lower  animals  for  ten  minutes  can 
scarcely  fail  to  see  the  method  exemplified.  If  he  were  watching  a  chick 
pecking  at  a  variety  of  objects  and  giving  signs  of  disgust  when  it  had 
seized  a  nauseous  substance,  he  would  doubtless  regard  the  process  as 
one  of  trial  and  error,  whatever  name  he  might  apply  to  it.  A  study  of 
the  conduct  of  much  lower  organisms  would  disclose  many  cases  almost 
equally  evident.  The  lives  of  most  insects,  crustaceans,  worms,  and 
hosts  of  lower  invertebrate  forms,  including  even  the  Protozoa,  show  an 
amount  of  busy  exploration  that  in  many  cases  far  exceeds  that  made 
by  any  higher  animal.  Throughout  the  animal  kingdom  there  is  obedi- 
ence to  the  Pauline  injunction,  '  Prove  all  things,  hold  fast  to  that  which 
is  good  '"  (I.e.,  p.  108). 

The  well-known  behavior  of  hermit  crabs  in  finding  suitable  shells 
in  which  to  live  and  in  changing  shells  which  have  become  unsuitable 
shows  a  systematic  application  of  the  method  of  trial  extending  to  the 
details  of  the  behavior.  This  is  well  brought  out  in  the  excellent  analysis 
of  this  behavior  given  by  Bohn  (1903). 

Behavior  of  higher  animals  based  on  the  selection  of  the  results  of 
varied  movements  —  the  "method  of  trial  and  error"  —  plays,  as  is 
well  known,  a  large  part  in  recent  discussions  of  that  subject.  The 
work  of  Thorndike  (1898)  on  behavior  in  the  cat,  and  the  books  of 
Lloyd  Morgan  (1900),  in  which  this  matter  is  dealt  with,  are,  of  course, 
well  known,  and  require  no  discussion  on  our  part.  The  fact  that  be- 
havior of  this  character  plays  a  large  part  in  higher,  as  well  as  in  lower, 
organisms,  is  of  the  greatest  interest,  as  showing  that  this  method  is 
one  of  fundamental  and  general  importance.  But  with  the  details  in 
higher  animals  we  are  not  here  concerned. 

3.      MODIFIABILITY   OF    BEHAVIOR   AND    ITS    DEPENDENCE   ON   PHYSIO- 
LOGICAL States 

In  the  section  preceding  the  present  one  we  have  described  many 
cases  of  behavior  in  the  lower  invertebrates  in  which  the  animal,  under 
the  action  of  constant  external  conditions,  passes  from  one  form  of  be- 
havior to  another.  All  such  cases  are  illustrations  of  the  fact  that  be- 
havior depends  upon  internal,  physiological  conditions,  as  well  as  upon 
external  stimuli.  Since  under  the  same  external  conditions  the  action 
changes,  the  animal  must  itself  have  changed,  otherwise  it  could  not  now 
behave  differently  from  before.  It  is  clear  that  the  continuance  of  a 
stimulus,  or  the  performance  of  a  certain  action,  may  change  the  physio- 
logical state  of  the  animal  so  as  to  induce  new  reactions. 

In  some  cases  the  varied  actions  performed  under  stimulation  have 


BEHAVIOR  IN  LOWER  METAZOA  251 

been  spoken  of  as  random  movements  (Holmes,  1905).  The  word 
"random,"  of  course,  implies  only  that  these  movements  are  not  defined 
by  the  position  of  the  stimulus;  it  does  not  signify  that  the  move- 
ments are  undetermined.  The  principle  of  cause  and  effect  applies  to 
these  movements  as  well  as  to  others.  But  the  causes  lie  partly  within 
the  animal;  each  phase  of  the  movement  aids  in  determining  the  suc- 
ceeding phase.  The  earthworm  may  turn  to  the  right  at  a  given  instant 
merely  because  it  has  just  before  turned  to  the  left.  Reactions  in  which 
a  succeeding  phase  is  determined  by  a  previous  one  have  sometimes  been 
called  chain  reflexes  (Loeb,  1900;  Driesch,  1903).  If  this  term  is  used, 
it  needs  to  be  kept  in  mind  that  in  most  cases  the  succeeding  phase  is  not 
invariably  and  irrevocably  called  up  by  the  preceding  one,  as  is  implied 
by  this  term.  On  the  contrary,  the  relation  between  the  two  is  extremely 
variable.  One  type  of  action  may  be  repeated  many  times  before  the 
second  type  comes  into  play,  and  the  order  of  the  different  actions  is  by 
no  means  always  the  same.  Thus  the  preceding  phase  is  only  one  factor 
in  deciding  what  shall  be  the  present  action.  The  latter  depends  upon 
the  entire  physiological  state  of  the  organism,  which  is  determined  by 
various  factors.  Illustrations  of  this  are  seen  in  the  righting  reaction  of 
the  starfish  and  many  other  animals ;  in  the  series  of  reactions  by  which 
Stentor  responds  to  a  mass  of  carmine  grains  in  the  water  (p.  174);  in 
that  by  which  Stoichactis  gets  rid  of  waste  matter  lying  on  thedisk  (p.  202), 
and  the  like. 

The  diverse  physiological  states  of  lower  organisms  have  been  little 
studied.  This  is  partly  because  it  is  rarely  possible  to  observe  them  di- 
rectly; it  is  only  through  their  effects  upon  action  that  they  become 
evident.  Thus  the  real  data  of  observation  are  the  actions ;  if  we  con- 
sidered these  alone,  we  could  only  state  that  a  given  organism  reacts  under 
the  same  external  conditions  sometimes  in  one  way,  sometimes  in  another. 
This  would  give  us  nothing  definite  on  which  to  base  a  formulation  and 
analysis  of  behavior,  so  that  we  are  compelled  to  assume  the  existence 
of  changing  internal  states.  This  assumption,  besides  being  logically 
necessary,  is,  of  course,  supported  by  much  positive  evidence  drawn  from 
diverse  fields,  and  there  is  reason  to  believe  that  in  time  we  shall  be  able 
to  study  these  states  directly.  Before  we  can  come  to  a  full  understand- 
ing of  behavior,  we  shall  have  to  subject  the  physiological  states  of 
organisms  to  a  detailed  study  and  analysis,  as  to  their  objective  nature, 
causes,  and  effects. 

The  most  noticeable  and  therefore  best-known  physiological  states 
of  lower  animals  are  those  which  depend  upon  changes  in  metabolism. 
The  reactions  of  the  starfish  and  the  planarian  to  many  chemical  and 
mechanical  stimuli   depend,   like  those  of   the   sea    anemone,  on  the 


252  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

progress  of  metabolism.  Hungry  animals  react  positively  to  possible 
food,  while  satiated  ones  react  negatively  to  the  same  stimuli.  This 
most  significant  relation  is,  of  course,  almost  universal  in  organisms ; 
it  shows  directly  the  dependence  of  behavior  on  the  relation  of  external 
agents  to  internal  processes. 

V.  Uexkull  has  made  precise  studies  of  certain  physiological  states 
and  of  the  factors  on  which  they  depend,  in  the  sea  urchin  and  a  number 
of  other  lower  animals.  In  the  sea  urchin,  some  of  the  pedicellarise 
will  not  close  in  response  to  a  mechanical  stimulus,  save  in  case  this  has 
been  preceded  by  a  chemical  stimulus.  The  latter  changes  the  physio- 
logical state  of  the  protoplasm  (muscle  or  nerve),  so  that  it  now  reacts 
to  a  stimulus  which  before  would  have  had  no  effect.  The  spines  of  the 
sea  urchin  usually  bend  toward  a  spot  on  the  surface  of  the  body  that  is 
mechanically  stimulated,  as  by  a  needle.  But  if  this  stimulus  has  been 
preceded  by  the  action  of  a  chemical,  the  spines  now  reverse  the  reaction 
and  bend  away  from  the  region  stimulated.  Many  such  changes  in 
physiological  state  are  brought  by  v.  Uexkull  under  the  heading  of 
changes  in  tonus  of  the  muscles  or  nerves.  Steady  tension,  such  as  is 
produced  in  certain  muscles  by  pressing  a  spine  of  the  sea  urchin  to  one 
side,  decreases  the  tonus,  so  that  the  muscles  are  no  longer  so  tense  as 
before.  Such  muscles  react  more  readily  to  stimuli  than  do  those  of 
higher  tonus.  Sudden  jarring  produces  the  opposite  effect,  the  muscles 
pull  harder  and  react  less  readily  than  before.  Decrease  of  tonus  caused 
by  tension  is  transmitted  in  some  way  to  neighboring  spines,  so  that 
after  a  certain  spine  has  been  pressed  to  one  side,  all  those  about  it  bend 
in  the  same  direction  and  react  more  readily  than  before.  These  changes 
in  physiological  state  play  a  large  part  in  determining  the  behavior  of 
the  sea  urchin  under  natural  conditions. 

Besides  such  changes,  there  are  in  the  sea  urchin  others  that  are  less 
easy  to  formulate,  and  that  have  not  been  analyzed.  V.  Uexkull  found 
that  the  set  reflexes  of  the  spines  and  the  changes  in  tonus  mentioned 
above  impose  on  the  sea  urchin  a  behavior  that  under  most  conditions 
seems  stereotyped  and  predictable.  This  leads  the  author  named  to 
contrast  the  sea  urchin  as  a  "republic  of  reflexes"  with  higher  animals 
in  which  the  behavior  is  unified.  But  the  difference  is  only  one  of  de- 
gree. If  the  sea  urchin  is  placed  on  its  back,  the  usual  reflexes  and  their 
stereotyped  interrelations  would  not  restore  the  animal  to  the  natural 
position,  but  merely  cause  it  to  walk  forward  while  lying  on  its  back. 
As  a  result,  we  find  a  physiological  state  induced  that  causes  a  thorough- 
going change  in  the  behavior  of  the  spines.  They  now  move  in  such  a 
way  as  to  turn  the  sea  urchin  again  on  its  ventral  surface.  As  v.  Uex- 
kiill  says,  the  behavior  of  the  spines  is  variable  and  capable  of  adapta- 


BEHAVIOR   IN  LOWER   METAZOA  253 

tion  ("variabel  und  anpassungsfahig,"  1900,  p.  98).  This  adaptation, 
under  unusual  conditions,  of  the  movements  of  the  spines  to  the  needs  of 
the  organism  as  a  whole,  seems  to  remove  all  difference  in  principle 
between  the  behavior  of  the  sea  urchin  and  that  of  higher  animals. 

Many  illustrations  of  varied  physiological  states  could  be  given  from 
an  analysis  of  the  behavior  of  the  starfish  in  the  righting  reaction,  and 
in  the  various  experiments  devised  by  Preyer  (see  p.  239). 

In  the  flat  worm  Planaria  the  work  of  Pearl  (1903)  shows  that  the  be- 
havior depends  largely  upon  the  physiological  state.  In  this  animal  the 
following  different  states  determining  behavior  may  be  distinguished :  — 

1.  Conditions  of  hunger  and  satiety,  determining  the  reactions  to 
food  in  a  regulatory  way. 

2.  A  resting  or  "sleeping"  condition.  The  animal  is  often  found 
lying  quietly  under  rocks,  the  muscles  relaxed.  In  this  condition  it 
fails  to  react  to  weak  stimuli,  but  strong  stimulation  induces  the  negative 
reaction,  followed  by  continued  activity. 

3.  The  condition  of  normal,  undisturbed  activity.  The  animal  now 
responds  to  weak  stimuli  of  all  sorts  by  the  positive  reaction,  turning 
toward  the  side  stimulated,  while  strong  stimuli  cause  the  negative 
reaction. 

4.  A  condition  of  heightened  activity,  in  which  the  worm  makes 
many  "testing"  movements  with  the  head,  and  reacts  positively  to  most 
stimuli,  whether  strong  or  weak.  In  this  condition  the  planarian  makes 
the  appearance  of  actively  seeking  something,  and  of  following  up  any 
source  of  stimulation  which  it  finds. 

5.  An  "excited"  condition,  produced  by  stimulating  the  animal 
strongly  and  repeatedly.  In  this  condition  the  animal  moves  about  vio- 
lently and  reacts  negatively  to  most  stimuli  to  which  it  reacts  at  all. 

6.  Possibly  due  to  an  accentuation  of  the  condition  last  described  is 
a  change  of  reaction  observed  by  Pearl  when  one  side  of  the  head  of  an 
excited  specimen  is  stimulated  by  repeated  blows.  At  first  the  animal 
turns  farther  and  farther  away  from  the  side  stimulated.  Then  suddenly 
it  jerks  strongly  backward,  and  turns  far  in  a  direction  opposite  its 
previous  turning  —  that  is,  toward  the  side  stimulated.  "The  reaction 
appears  as  if,  after  the  animal  had  tried  in  vain  to  get  away  from  an  un- 
comfortable stimulus  by  its  ordinary  reaction,  it  finally  tries  a  wild  jump 
in  the  opposite  direction"  (Pearl,  1903,  p.  580). 

The  different  physiological  conditions  are  determined  largely  by  the 
history  of  the  individual  worm,  so  that  in  this  sense  its  behavior  may  be 
said  to  depend  on  its  experience.  The  dependence  of  the  reactions  on 
the  physiological  state  is  in  a  given  specimen  very  great,  so  that  two  in- 
dividuals often  react  in  opposite  ways  to  the  same  stimulus.     The  same 


254  BEHAVIOR  OF   THE   LOWER   ORGANISMS 

individual  that  reacts  to  a  given  stimulus  positively  may  a  little  later 
react  negatively,  and  vice  versa.  After  long  study  of  Planaria,  Pearl 
concludes  that  "it  is  almost  an  absolute  necessity  that  a  person  should 
become  familiar,  or  perhaps  better,  intimate,  with  an  organism,  so  that 
he  knows  it  in  something  the  same  way  that  he  knows  a  person,  before 
he  can  hope  to  get  even  an  approximation  of  the  truth  regarding  its 
behavior."     This  remark  might  be  extended  to  most  lower  animals. 

As  we  have  seen  in  a  previous  section  (p.  236),  the  behavior  of  the 
flatworm  shows  certain  well-defined  reaction  types,  which  might,  taken 
separately,  be  called  reflexes.  But  when  we  consider  the  various  factors 
which  determine  the  production  and  combination  of  these  reaction  types, 
we  cannot  consider  the  behavior  of  the  flatworm  as  "purely  reflex," 
if  we  mean  by  reflexes  invariable  reactions  to  the  same  external  stimuli. 
On  the  contrary,  the  behavior  is  extremely  variable  in  accordance  with 
many  conditions,  internal  as  well  as  external. 

A  detailed  analysis  of  the  behavior  of  almost  any  of  the  lower  inver- 
tebrates would  show  as  many  different  physiological  conditions  on  which 
behavior. depends  as  we  find  in  the  flatworm.  In  the  earthworm,  for 
example,  the  conditions  are  still  more  complicated  than  in  the  flatworm, 
so  that  the  same  external  stimulus,  acting  with  the  same  intensity,  and 
applied  to  the  same  spot  on  the  body,  may  produce  any  one  of  at  least 
six  different  reactions.  The  variations  of  internal  state  as  the  animal 
moves  about  are  what  condition  the  "random  movements"  described 
by  Holmes  in  the  reactions  to  light,  and  by  Smith  in  the  reactions  to  other 
stimuli  (see  p.  247). 

Of  special  interest  are  changes  in  state  that  lead  to  more  or  less  per- 
manent modifications  in  behavior.  These  are  little  known  in  the  lower 
organisms.  Most  of  the  changes  of  physiological  state  described  in  the 
foregoing  paragraphs  are  not  known  to  last  more  than  a  short  time. 
In  Vorticella,  Hodge  and  Aikins  (1895)  state  that  the  modified  behavior 
endured  for  five  hours ;  this  perhaps  needs  confirmation.  In  the  lowest 
organisms  it  is  difficult  to  carry  out  experiments  that  shall  determine 
how  long  modifications  last.  Perhaps  the  lowest  animal  in  which  an 
enduring  modification  of  behavior  has  been  demonstrated  is  the  flatworm 
Convoluta  roscoffensis.  This  is  one  of  the  lowest  of  the  group,  belong- 
ing to  the  division  Accela,  which  includes  the  simple  forms  having  no 
alimentary  canal.  The  behavior  of  Convoluta,  as  described  by  Gamble 
and  Keeble  (1903),  and  by  Bohn  (1903  a),  presents  many  features  of 
the  greatest  interest ;  into  only  a  few  of  these  can  we  enter.  Convoluta 
is  a  small  green  worm  that  lives  in  immense  numbers  on  the  sand  of  the 
seacoast  of  Brittany,  just  above  the  water  line.  It  forms  thus  large 
green  patches.     When  the  tide  rises  the  water  covers  the  region  where 


BEHAVIOR  IN  LOWER   METAZOA 


255 


Convoluta  is  found,  and  the  waves  would  wash  the  animals  away,  if 
their  behavior  did  not  prevent.  As  the  water  rises  and  the  waves  begin 
to  beat  on  the  sand  near  them,  they  go  downward  into  the  sand,  where 
they  are  protected.  As  the  water  sinks,  the  animals  creep  upward  and 
appear  again  at  the  surface.  These  upward  and  downward  movements 
are  reactions  with  reference  to  gravity,  as  is  shown  by  placing  the  animals 
on  smooth,  inclined,  or  perpendicular  surfaces.  They  go  downward 
as  the  tide  rises,  upward  as  it  falls.  Bohn  (1905)  has  shown  that  many 
littoral  mollusks  and  annelids  show  similar  movements  with  relation  to 
the  tides. 

The  peculiarly  interesting  fact  concerning  this  behavior  in  Convoluta 
is  the  following:  This  periodical  alternation  of  reactions,  produced  by 
an  environmental  factor,  becomes  so  impressed  on  the  organization  of 
the  animal  that  it  occurs  even  when  this  factor  is  lacking.  The  alterna- 
tion of  movement  has  become  habitual.  If  the  worms  are  removed 
to  an  aquarium  where  the  tide  no  longer  acts  upon  them,  they  continue 
to  go  downward  at  the  period  of  high  tide,  upward  at  the  period  of  low 
tide.  This  continues  for  about  two  weeks,  so  that  the  worms  may  be 
carried  far  away  from  the  shore,  and  may  then  be  used  for  a  time  as  tide 
indicators.  But  under  such  conditions  the  periodicity  after  a  time  dis- 
appears, showing  that  it  was  really  due  to  the  external  factor,  —  the  tides. 
This  appears  to  be  the  lowest  known  case  of  what  we  call  in  higher 
animals  a  habit. 

In  some  of  the  higher  invertebrates,  lasting  modifications  of  behavior 
of  a  still  more  complex  character  may  be  induced  experimentally.  This 
has  been  accomplished  in  the  Crustacea  by  Yerkes  (1902),  Yerkes  and 
Huggins  (1903),  and  Spaulding  (1904). 

With  the  crayfish  and  crab,  Yerkes  and  Huggins  (1903)  studied 
the  modification  of  behavior  in  escaping  from  danger  and  in  finding 
water.  The  crayfish  was  placed  in  one 
end  of  an  inclined  pen  which  opened  at 
the  other  end  into  the  water.  The  pen 
was  partly  divided  by  partitions  in  such  a 
way  as  to  leave  two  passages  leading  to 
the  water  (Fig.  139).  Either  of  these  pas- 
sages could  be  closed  at  its  end  by  a  glass 
plate   G.    The  animal  was  placed  at   T 

(Fig.     139).      In     moving    away   from    this      After  Yerkes.     See  text 

region  it  might  enter  the  blind  pocket  at  G,  thus  not  directly  reaching  the 
water,  or  it  might  go  through  the  other  passage  straight  to  the  water. 

After  some  preliminary  experiments  without  closing  either  passage, 
showing  that  the  animals  were  as  likely  to  pass  to  the  right  as  to  the  left, 


Fig.  139.  —  Pen  used  by  Yerkes 
in    experimenting    with     Crustacea. 


256  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

the  partition  was  placed  in  the  right  passageway,  as  in  Fig.  139.  The 
crayfish  which  turned  to  the  left  on  leaving  T  escaped  at  once  to  the  water. 
But  if  it  turned  to  the  right  it  passed  into  the  pocket  G,  and  was  compelled 
to  explore  the  region,  finally  turning  to  the  left  and  passing  the  partition 
P,  before  it  could  escape.  Three  individuals  were  given  sixty  trials  each 
in  the  course  of  thirty  days.  In  the  first  ten  trials  they  went  just  as  fre- 
quently into  the  blind  passage  as  toward  the  water.  In  the  second  ten 
trials,  the  animals  started  in  60  per  cent  of  the  cases  toward  the  open 
passage  at  the  left.  In  the  next  ten  trials  this  proportion  had  risen  to 
75.8  per  cent;  in  the  following  ten,  to  83.3  per  cent.  In  the  last  ten 
trials  of  the  sixty,  very  few  mistakes  were  made.  In  90  per  cent  of  all 
cases  they  went  straight  for  the  open  passage.  In  another  series  of 
experiments  an  individual,  after  four  hundred  trials,  made  only  one 
mistake  in  fifty  trials.  Similar  results  were  obtained  by  Yerkes  (1902) 
in  experimenting  on  the  crab  Carcinus  granulatus. 

Thus  at  the  beginning  of  the  experiment  the  animals  were  as  likely 
to  go  to  the  right  as  to  the  left,  while  at  the  end  they  went  almost  inva- 
riably to  the  left.  Since  the  external  conditions  had  not  changed,  the 
animals  themselves  must  have  changed.  Their  internal  condition  now 
differed  in  some  way  from  the  original  condition. 

Yerkes  and  Huggins  (1903)  endeavored  to  determine  how  easily 
this  acquired  condition  could  be  modified  or  destroyed.  After  the  cray- 
fish had  learned  to  go  through  the  open  passageway  so  as  to  make  a  mis- 
take in  only  one  case  in  ten,  the  experiments  were  discontinued  for  two 
weeks.  On  the  fourteenth  day  the  animals  were  still  inclined  to  go 
straight  to  the  open  passage,  though  the  habit  had  become  dulled,  and 
they  now  made  mistakes  in  about  three  cases  out  of  ten. 

In  other  experiments,  after  the  animals  had  acquired  the  habit  of 
escaping  through  the  right  passage,  the  partition  G  was  changed,  so  as  to 

block  up  this  passage,  but 
leave  the  left  one  open. 
At  the  next  trial  the  ani- 
mal made  a  long-continued 
attempt  to  escape  by  the 
right-hand  passageway,  fol- 
lowing the  path  shown   in 

Fig.   140.  —  Path  followed  by  a  crayfish  which  has  Yw        IJ.O  It      Wandered 

formed  the  habit  of  escaping  to  the  water   by  the    right-  &" 

hand  passageway,   when  this  passage  is  closed   and  the  about      tor     utteeil     minutes 

left  one  opened.     After  Yerkes  and  Huggins.  before  disCOVCrino"  the  Open 

way.  But  in  the  next  trial  it  turned  to  the  left,  and  thereafter  it 
turned  almost  as  regularly  to  the  left  as  it  had  before  turned  to  the 
right. 


BEHAVIOR   IN   LOWER   METAZOA 


257 


This  habit  formation  took  place  in  the  same  manner  when  the  floor 
of  the  pen  was  carefully  washed  out  after  each  trial,  showing  that  the 
animals  were  not  merely  following  a  path  marked  by  an  odor  from  the 
previous  passage  along  it.  It  was  evident  that  the  customary  direction 
of  turning  played  a  large  part  in  the  behavior.  When  the  left  passage 
was  closed,  the  crayfish  that  had  erred  into  this  passage  escaped  by  turn- 
ing to  the  right,  as  indicated  by  its  path  in  Fig.  141.  When  after  the 
establishment  of  this  habit,  the  right  passage  was  closed  (Fig.  140), 
the  animal  tried  persistently  to  escape  from  this  passage  by  turning  to 
the  right,  as  it  had  previously  done. 

Spaulding  (1904)  studied  the  modifiability  of  behavior  in  the  food 
reactions  of  the  hermit  crab.  These  animals  tend  to  remain  in  the  lighted 
parts  of  the  aquarium.  They  were  fed  by  placing  a  small,  dark  screen 
with  a  fish  beneath  it  in  a  certain  part  of  the  aquarium.  The  diffusion 
of  juices  from  the  fish  set  the 
crabs  to  moving  about  ac- 
tively, and  in  the  course  of 
time  some  passed  beneath 
the  screen.  Here  the  food 
was  found.  At  first  it  took 
the  crabs  a  long  time  to  find 
it  under  these  conditions. 
On  the  first  day  only  three 
out  of  thirty  succeeded  in 
fifteen  minutes.     But  by  the 


Fig.  141.  —  Path  followed  by  crayfish  while  being 
trained  to  avoid  the  left  passage.  On  erring  into  this 
passage,  it  escapes  by  passing  to  the  right,  thus  forming 
the  habit  of  turning  to  the  right.  After  Yerkes  and 
Huggins. 


third  day,  twenty  of  the  thirty  had  passed  beneath  the  screen  fifteen 
minutes  after  it  was  introduced.  At  the  end  of  the  eighth  day,  twenty- 
eight  out  of  the  twenty-nine  present  had  passed  beneath  the  screen 
inside  of  five  minutes.  The  crabs  had  become  so  modified  that  they 
went  quickly  beneath  the  screen  as  soon  as  it  was  introduced. 

Now  the  experiments  were  varied  by  placing  in  the  aquarium  the 
screen  alone,  without  the  food.  Most  of  the  animals  passed  beneath 
it  as  before.  Thus,  on  the  thirteenth  day  of  the  experiments,  twenty- 
five  specimens  out  of  twenty-seven  present  had  passed  under  the  screen 
within  five  minutes.  After  they  had  entered  they  were  fed,  in  order  that 
the  association  between  the  screen  and  food  might  not  be  destroyed. 

Phenomena  of  this  character  are  usually  spoken  of  as  learning,  or 
as  the  formation  of  habits  or  associations.  The  facts  may  be  expressed 
in  a  purely  objective  way  as  follows:  When  subjected  to  the  stimulus 
of  the  screen  and  the  food,  the  animals  reacted  to  the  food  by  gathering 
about  it  —  incidentally  of  course  gathering  under  the  screen.  After 
many  repetitions  of  such  stimulation,  the  animals  had  become  changed 


258  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

so  that  they  responded  to  the  dark  screen  alone  by  the  reaction  proper 
to  food.  We  shall  analyze  these  phenomena  more  fully  in  our  general 
discussion  of  behavior  (Chapter  XVI). 

These  processes,  by  which  behavior  becomes  more  or  less  enduringly 
modified,  are  known  to  play  a  large  part  in  the  behavior  of  higher  inver- 
tebrates, such  as  ants  and  bees,  and  in  the  vertebrates.  As  investigation 
progresses,  we  find  analogous  processes  lower  and  lower  in  the  animal 
scale.  It  was  only  eight  years  ago  that  Bethe  (1898)  could  deny  their 
occurrence  even  in  ants  and  bees ;  now  they  have  been  fully  demonstrated 
in  these  and  much  lower  animals.  The  study  of  these  matters  has  hardly 
begun,  and  it  is  not  too  much  to  say  that  no  experiments  have  been 
carried  through  on  the  lowest  invertebrates  that  would  show  this  lasting 
modifiability,  even  if  it  exists.  We  are  therefore  still  in  the  dark  as  to 
how  far  downward  such  modifiability  extends;  time  may  show  it  to  be 
a  universal  property  of  living  things. 

The  importance  of  this  modifiability  for  the  understanding  of  behavior 
is  obviously  great.  Where  such  modifiability  exists,  the  definite  "  reflex" 
is  not  to  be  considered  a  permanent,  final  element  of  behavior.  On  the 
contrary,  it  is  something  developed,  and  it  must  differ  in  individuals 
with  different  histories.  Two  specimens  of  Convoluta  side  by  side  might 
show  at  the  same  moment,  one  "positive  geotropism,"  the  other  "nega- 
tive geotropism,"  depending  on  their  past  history.  Whether  a  hermit 
crab  will  pass  beneath  a  dark  screen,  or  will  avoid  it,  is  not  determined 
by  the  permanent  properties  of  its  colloidal  substance;  this  can  be  pre- 
dicted only  by  knowing  the  history  of  the  individual. 

The  process  by  which  an  organism  acquires  a  definite  reaction  which 
it  before  had  not  is,  of  course,  nothing  mystical,  but  an  actual  physio- 
logical one,  whose  progress  is  open  to  investigation  as  is  that  of  any  other. 
It  needs  to  be  studied  and  analyzed  in  the  same  objective  way  as  the 
circulation  of  the  blood.  The  power  of  changing  when  acted  upon  by 
outer  agents,  in  such  a  way  as  to  react  differently  thereafter,  is  one  of  the 
most  important  properties  of  living  matter,  and  it  is  misleading  to  ignore 
this  property  and  deal  with  animals  as  if  their  reactions  were  invariable. 
How  the  modifications  occur  is  one  of  the  fundamental  problems  of 
physiology.  We  must  remember  that  even  what  we  call  memory,  in- 
telligence, and  reasoning  are  composed  objectively  of  certain  physio- 
logical processes.  In  other  words,  as  Liebmann  has  emphasized,  there 
are  objective  material  processes  that  follow  the  laws  of  intelligence,  of 
reasoning,  of  logic.  This  is  a  capital  fact.  In  searching  for  the  laws  of 
life  processes  we  must  remember  that  those  just  mentioned  are  as  real  as 
any  others,  and  their  laws  must  be  provided  for  in  the  physics  and 
chemistry  of  colloids  if  these  are  to  give  us  the  laws  of  life  processes. 


BEHAVIOR  IN  LOWER   METAZOA  259 

We  shall  attempt  to  analyze  some  of  these  matters  farther  in  our  general 
discussion  of  behavior,  which  forms  the  remainder  of  the  work. 

LITERATURE  XII 

A.  Behavior  of  echinoderms :  Uexkull,  1897,  1897  a,  1899,  1900,  1900  a ; 
Preyer,  1886;  Romanes,  1885. 

B.  Behavior  of  planarians  :  Pearl,  1903  ;  Mast,  1903. 

C.  Behavior  of  Rotifera :  Jennings,  1904  b. 

D.  Reaction  by  varied  movements  in  other  invertebrates  :  Smith,  1902  ;  Holmes, 
1905;  Bohn,  1903;  Moebius,  1873;  Harper,  1905. 

E.  Method  of  trial  and  error  in  vertebrates  :  Thorndike,  1898;  Morgan,  1900. 

F.  Modifiability  of  behavior  in  lower  animals:  Bohn,  1903  a,  1905;  Gamble 
and  Keeble,  1903;  Jennings,  1904  d  ;  Yerk.es,  1902;  Yerkes  and  Huggins, 
1903;   Spaulding,  1904. 


PART   III 

ANALYSIS    OF     BEHAVIOR     IN     LOWER     ORGANISMS, 
WITH    A   DISCUSSION   OF   THEORIES 

CHAPTER   XIII 

COMPARISON   OF   BEHAVIOR   OF   UNICELLULAR   AND   MULTI- 
CELLULAR  ORGANISMS 

We  have  now  examined  the  behavior  of  a  number  of  Protozoa  and 
of  a  number  of  Metazoa.  What  characteristic  differences  do  we  find 
between  the  two? 

This  question  is  of  interest  from  a  number  of  points  of  view.  The 
Protozoa  consist  each  of  but  a  single  cell,  while  the  Metazoa  are  com- 
posed of  many  cells,  which  are  differentiated  for  the  performance  of 
different  functions.  Does  this  difference  in  structure  correspond  to  any 
fundamental  difference  in  behavior?  Le  Dantec  (1895)  proposed  to 
distinguish  the  life  manifestations  of  the  Protozoa  as  "  elemental  life  ': 
from  the  life  of  the  Metazoa,  holding  that  the  two  are  so  different  in 
fundamental  character  that  it  is  improper  to  apply  the  same  name  to 
them ;  this  point  of  view  is  often  met  in  scientific  literature.  The  life 
of  the  Protozoa  is  considered  "as  the  direct  result  of  the  diverse  reactions 
of  a  small  mass  of  a  certain  chemical  substance  in  the  presence  of  appro- 
priate substances  "  {I.e.,  p.  26),  while  that  of  the  Metazoa  is  "  the  result 
of  the  functioning  of  an  extremely  complicated  machine,  in  which  the 
reactions  of  the  chemical  in  question  serve  as  motor  power."  The 
former  is  compared  to  the  burning  of  the  alcohol  in  an  alcohol  motor, 
the  latter  to  the  functioning  of  the  motor  itself  (p.  27).  We  are  inter- 
ested in  the  question  whether  this  theoretically  fundamental  difference 
shows  itself  in  any  way  in  the  phenomena  to  be  observed.  Is  there  any 
objective  evidence  in  the  behavior  for  the  belief  that  the  life  of  the  Pro- 
tozoa differs  fundamentally  from  that  of  the  Metazoa? 

Again,  the  Metazoa  possess  a  nervous  system,  while  the  Protozoa 
have  none.  To  the  specific  properties  of  the  nervous  system  many  of 
the  manifestations  of  behavior  in  higher  animals  have  been  attributed. 
This  system  is  often  considered  an  essential  prerequisite  for  certain 

260 


s 


COMPARISON   OF  PROTOZOA    AND  METAZOA  261 

fundamental  features  of  behavior.  Do  we  find  a  striking  difference  in 
the  behavior  of  organisms  after  a  nervous  system  has  been  developed  ? 
What  can  animals  do  without  a  nervous  system?  A  comparison  of 
organisms  with  and  those  without  this  system  should  give  us  evidence  as 
to  the  real  nature  of  the  functions  of  the  latter,  and  will  perhaps 
prevent  us  from  overestimating  its  importance. 

We  will  sum  up  briefly  in  a  number  of  paragraphs  the  resemblances 
and  differences  between  the  behavior  of  animals  with  and  without  a 
nervous  system. 

1.  First,  we  find  that  in  organisms  consisting  of  but  a  single  cell, 
and  having  no  nervous  system,  the  behavior  is  regulated  by  all  the  dif- 
ferent classes  of  conditions  which  regulate  the  behavior  of  higher  animals. 
In  other  words,  unicellular  organisms  react  to  all  classes  of  stimuli  to 
which  higher  animals  react.1  All  classes  of  stimuli  which  may  affect 
the  nervous  system  or  sense  organs  may  likewise  affect  protoplasm 
without  these  organs.  Even  the  naked  protoplasm  of  Amoeba  responds 
to  all  classes  of  stimuli  to  which  any  animal  responds.  The  nervous 
system  and  sense  organs  are  therefore  not  necessary  for  the  reception  of 
any  particular  classes  of  stimulations. 

2.  The  reactions  produced  in  unicellular  organisms  by  stimuli  are 
not  the  direct  physical  or  chemical  effects  of  the  agents  acting  upon  them, 
but  are  indirect  reactions,  produced  through  the  release  of  certain  forces 
already  present  in  the  organism.  In  this  respect  the  reactions  are  com- 
parable with  those  of  higher  animals.  This  is  true  for  Amoeba  as  well 
as  for  more  differentiated  Protozoa. 

3.  In  the  Protozoa,  as  in  the  Metazoa,  the  structure  of  the  organism 
plays  a  large  part  in  determining  the  nature  of  the  behavior.  There  are 
only  certain  acts  which  the  organism  can  perform,  and  these  are  condi- 
tioned by  its  organization ;  by  one  of  these  acts  it  must  respond  to  any 
stimulus.  If  the  behavior  of  the  Metazoa  is  comparable  in  this  respect 
to  the  action  of  a  machine,  the  same  comparison  can  be  made  for  the 
behavior  of  the  Protozoa. 

4.  Spontaneous  action  —  that  is,  activity  and  changes  in  activity 
induced  without  external  stimulation  —  takes  place  in  the  Protozoa 
as  well  as  in  the  Metazoa.  Both  Vorticella  and  Hydra,  as  we  have  seen, 
spontaneously  contract  at  rather  regular  intervals,  even  when  the  external 
conditions  remain  uniform.  Continued  activity  is  the  normal  state  of 
affairs  in  Paramecium  and  most  other  infusoria.  The  idea  that  spon- 
taneous activity  is  found  only  in  higher  animals  is  a  totally  erroneous 
one ;   action  is  as  spontaneous  in  the  Protozoa  as  in  man. 

1  Considering  auditory  stimulation  as  merely  a  special  case  of  mechanical  stimulation. 


262  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

5.  In  unicellular  organisms,  without  a  nervous  system,  certain  parts 
of  the  body  may  be  more  sensitive  than  the  remainder,  forming  thus  a 
region  comparable  to  a  sense  organ  in  a  higher  animal.  Whether  such 
a  part  may  become  more  sensitive  to  one  form  of  stimulation,  while 
insensitive  to  others,  as  in  higher  organisms,  seems  not  to  have  been 
determined. 

6.  Conduction  occurs  in  organisms  without  a  nervous  system.  This 
is,  of  course,  seen  in  the  fact  that  a  stimulus  limited  to  one  part  of  the 
body  may  cause  a  contraction  of  the  entire  body,  or  a  reversal  of  cilia 
over  the  entire  body  surface.  A  strongly  marked  case  is  the  contraction 
of  the  stalk  in  Vorticella,  when  only  the  margin  of  the  bell  is  stimulated. 

7.  Summation  of  stimuli  occurs  in  Protozoa  as  in  Metazoa.  This 
is  shown  most  clearly  in  Statkewitsch's  experiments  with  induction 
shocks  (p.  83).  Weak  induction  shocks  have  no  effect  until  frequently 
repeated. 

8.  In  the  unicellular  animal,  as  in  that  composed  of  many  cells,  the 
reaction  may  change  or  become  reversed  as  the  intensity  of  the  stimulus 
increases,  though  the  quality  of  the  stimulus  remains  the  same.  Such 
a  change  in  reaction  has  sometimes  been  claimed  as  a  specific  property 
of  the  nervous  system.  The  protozoans  Amoeba  and  Stentor,  as  well 
as  the  metazoan  Planaria,  move  toward  sources  of  weak  mechanical 
stimulation,  away  from  sources  of  strong  stimulation. 

9.  In  the  Protozoa,  as  in  the  Metazoa,  the  reaction  may  change  while 
the  stimulus  remains  the  same.  That  is,  the  animal  may  respond  at 
first  by  a  certain  reaction ;  later,  while  the  stimulus  remains  the  same, 
by  other  reactions.  This  has  been  shown  in  detail  in  the  account  of 
Stentor  (Chapter  X).  The  change  may  consist  in  either  a  cessation  of 
the  reaction,  or  in  a  complete  alteration  of  its  character.  These  changes 
are,  as  a  rule,  by  no  means  due  to  fatigue,  but  are  regulatory  in  character. 
The  behavior  thus  depends  on  the  past  history  of  the  organism.  For 
such  modifications  of  behavior  a  nervous  system  is  then  unnecessary. 

10.  In  the  Protozoa,  as  in  the  Metazoa,  the  reactions  are  not  invari- 
able reflexes,  depending  only  on  the  external  stimulus  and  the  anatomi- 
cal structure  of  the  organism.  The  reaction  to  a  given  stimulus  de- 
pends upon  the  physiological  condition  of  the  organism.  In  Stentor 
we  could  distinguish  at  least  five  different  conditions,  each  with  its  char- 
acteristic reaction  to  the  given  stimulus. 

11.  In  unicellular  as  well  as  multicellular  animals  we  find  two  chief 
general  classes  of  reactions,  which  may  be  designated  positive  and  nega- 
tive. The  positive  reaction  tends  to  retain  the  organism  in  contact 
with  the  stimulus,  the  negative  to  remove  it  from  the  stimulus.  In  many 
classes  of  stimuli  we  can  distinguish  an  optimum  condition.     A  change 


* 


COMPARISON   OF  PROTOZOA    AND  METAZOA  263 

leading  from  the  optimum  produces  a  negative  reaction,  while  a  change 
leading  toward  the  optimum  produces  no  reaction,  or  a  positive  one. 
The  optimum  from  this  standpoint  usually  corresponds,  in  a  broad 
way,  to  the  optimum  for  the  general  interests  of  the  organism.  These 
relations  hold  equally  for  Protozoa  and  Metazoa. 

12.  In  both  the  Protozoa  and  the  Metazoa  that  we  have  studied,  the 
behavior  is  based  to  a  considerable  degree  on  the  selection  of  certain 
conditions  through  the  production  under  stimulation  of  varied  move- 
ments (see  Chapter  XII).  This  shows  itself  in  two  characteristic  types. 
In  the  one  case  the  organism  when  subjected  to  a  change  leading  away 
from  the  optimum  responds  by  a  movement  that  subjects  it  successively 
to  many  different  conditions,  finally  remaining  in  that  one  which  is 
nearest  the  optimum.  This  form  of  reaction  is  strongly  developed  in 
Paramecium.  In  the  second  type,  which  may  be  considered  a  devel- 
opment of  the  first,  the  organism  first  responds  by  one  reaction,  then 
by  another,  continuing  at  intervals  to  change  its  response  until  one  of 
the  reactions  frees  it  from  the  stimulation.  This  way  of  behaving  is 
well  seen  in  Stentor.  Both  methods  of  reaction  may  be  expressed  as 
follows :  When  the  organism  is  subjected  to  an  irritating  condition,  it 
tries  many  different  conditions  or  many  different  ways  of  ridding  itself 
of  this  condition,  till  one  is  found  which  is  successful. 

All  together,  there  is  no  evidence  of  the  existence  of  differences  of  fun- 
damental character  between  the  behavior  of  the  Protozoa  and  that  of 
the  lower  Metazoa.  The  study  of  behavior  lends  no  support  to  the 
view  that  the  life  activities  are  of  an  essentially  different  character  in  the 
Protozoa  and  the  Metazoa.  The  behavior  of  the  Protozoa  appears  to 
b>e  no  more  and  no  less  machinelike  than  that  of  the  Metazoa ;  similar 
principles  govern  both. 

Further,  the  possession  of  a  nervous  system  brings  with  it  no  observ- 
able essential  changes  in  the  nature  of  behavior.  We  have  found  no 
important  additional  features  in  the  behavior  when  tl^e  nervous  system 
is  added.  In  the  lower  Metazoa,  experiment  has  shown  the  nervous 
system  to  have  two  chief  functions,  —  the  maintenance  of  tonus,  and  the 
bringing  of  the  parts  of  the  body  into  relation  with  each  other  by  serving 
for  conduction.  But  both  these  functions  are  performed  in  the  Protozoa 
without  a  nervous  system.  The  body  of  Paramecium  maintains  marked 
tonus,  and  the  different  parts  of  the  body  work  together.  A  comparison 
of  the  behavior  of  the  Protozoa  with  that  of  the  lower  Metazoa  lends 
powerful  support  to  that  view  of  the  functions  of  the  nervous  system 
which  is  so  ably  maintained  by  Loeb  in  his  brilliant  work  on  "The  Com- 
parative Physiology  of  the  Brain  and  Comparative  Psychology. "  Accord- 
ing to  this  view  we  do  not  find  in  the  nervous  system  specific  qualities 


1 


264  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

not  found  elsewhere  in  protoplasmic  structures.  The  qualities  of  the 
nervous  system  are  the  general  qualities  of  protoplasm.  Certain  of 
these  general  qualities  have  become  much  accentuated  in  the  protoplasm 
of  the  nervous  system,  while  in  the  remainder  of  the  protoplasm  of  the 
metazoan  body  they  are  less  strongly  marked,  being  partially  obscured 
by  differentiations  in  other  directions.  Most  if  not  all  of  the  funda- 
mental activities  which  have  been  considered  peculiar  to  the  nervous 
system  may  be  demonstrated,  as  we  have  seen,  in  the  Protozoa,  yet  in 
them  no  nervous  system  exists. 

These  facts  show  the  necessity  of  guarding  against  overrating  the 
importance  of  the  nervous  system.  It  is  doubtful  if  the  nervous  system 
is  to  be  considered  the  exclusive  seat  of  anything;  its  properties  are 
accentuations  of  the  general  properties  of  protoplasm.  Dogmatic  state- 
ments as  to  the  part  necessarily  played  by  the  nervous  system  in  given 
cases  must  be  looked  upon  with  suspicion  unless  supported  by  positive 
experimental  results.  If  acts  objectively  identical  with  "reflex  actions" 
and  still  more  complex  types  of  behavior  may  exist  in  the  Protozoa  with- 
out the  intervention  of  a  nervous  system,  it  is  not  impossible  that  they 
may  occur  in  the  same  manner  in  Metazoa,  as  Loeb  has  maintained. 
Where  a  nervous  system  exists,  we  are  not  justified  in  dogmatically  refer- 
ring all  phenomena  of  behavior  to  it,  for  other  protoplasm  exists  too,  and 
may  still  retain  some  of  the  characteristics  which  it  had  in  the  Protozoa. 
In  an  animal  possessing  a  nervous  system  we  cannot  tell  without  experi- 
mentation whether  a  given  reflex  action  or  other  reaction  depends  on 
the  nervous  system  or  not.  The  possibility  always  remains  open  that 
the  remainder  of  the  protoplasm  may  perform  the  act  in  question  by  its 
own  capabilities,  as  it  does  in  the  Protozoa.  In  any  animal,  we  are 
justified  in  attributing  exclusively  to  the  nervous  system  only  those  prop- 
erties which  rigid  analytical  experimentation  shows  it  alone  to  possess. 


- 


CHAPTER    XIV 

TROPISMS   AND   THE   LOCAL   ACTION   THEORY   OF   TROPISMS 

A  large  share  of  the  behavior  of  lower  as  well  as  of  higher  animals  j 
consists  of  movements  either  toward  or  away  from  certain  objects  or 
sources  of  stimulation.  Behavior  can  thus  be  largely  classified  into 
two  great  classes:  "positive  and  negative"  reactions;  movements  of 
"attraction  and  repulsion,"  of  approach  and  retreat.  To  account 
in  a  general  way  for  these  directed  movements  certain  theories  have 
been  proposed,  and  one  of  these  has  become  widely  accepted.  This  is 
the  so-called  "tropism  theory."  The  word  "tropism"  has  been  used  in 
several  different  senses  by  different  authors,  and  not  always  as  imply- 
ing a  definite  theory  (see  page  274).  But  there  is  a  certain  theory 
which  is  usually  implied  when  tropisms  are  mentioned;  it  has  become 
so  generally  accepted  that  it  is  often  spoken  of  as  the  tropism  theory. 
It  will  perhaps  be  more  accurate  to  speak  of  it  as  the  local  action^  theory 
of  tropisms.  "Tropisms"  has  become  the  key- word  for  the  behavior 
of  lower  organisms,  and  the  theory  mentioned  is  supposed  to  furnish 
explanation  of  most  of  the  puzzles  found  in  this  field.  A  theory  so 
generally  accepted  demands  separate  special  treatment.  What  is  this 
tropism  theory  as  usually  understood  in  discussions  of  animal  behavior, 
and  how  far  does  it  go  in  helping  us  to  understand  the  behavior  of  lower 
organisms  ? 

According  to  this  tropism  theory  the  primary  feature  in  the  directed 
movements  of  lower  organisms  is  the  position  or  orientation  of  the  body 
with  respect  to  the  source  of  stimulation,  and  this  orientation  is  brought 
about  by  the  direct  local  action  of  the  stimulating  agent  on  that  part  of 
the  body  on  which  it  impinges.  The  essential  points  in  this  theory  are 
then  two:  first,  orientation;  second,  the  production  of  orientation  by 
local  action.     These  points  we  may  consider  separately. 

(1)  By  this  tropism  theory  a  stimulus  is  considered  to  force  the 
animal  to  take  a  certain  position  with  respect  to  the  direction  from  which 
the  stimulus  comes;  in  this  position  it  is  said  to  be  oriented.  Usually 
the  organism  becomes  oriented  with  anterior  end  either  toward  or  away 
from  the  source  of  stimulation.  This  is  the  essential  feature  in  the  action 
of  the  stimulus.     "The  essential  point  in  all  directive  stimulation  is 

265 


266  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

therefore  the  axial  orientation  of  the  cell  body,  and  the  central  point  in 
the  mechanism  of  this  phenomenon,  lies  in  the  explanation  of  this  axial 
position"  (Verworn,  "General  Physiology,"  1899^.480).  After  the 
animal  has  thus  become  oriented  it  may  move  forward  in  the  usual 
way.  If  it  does  so,  it  will  of  course  incidentally  move  toward  or  away 
from  the  source  of  stimulation,  but  this  approach  or  retreat  is  not  an 
essential  or  determining  part  of  the  reaction.  "The  really  fundamental 
phenomenon  which  characterizes  these  directed  movements  is  always 
not  so  much  the  forward  movement  as  such,  as  rather  a  process  which 
may  be  called  a  movement  of  orientation.  The  organism  places  its 
axis  in  a  definite  localized  relation  to  the  stimulus,  which  may  be  photic, 
thermic,  chemical,  etc.  That  is,  it  places  its  axis  either  in  the  direction 
of  the  stimulation  or  perpendicular  to  it  (diatropism).  In  the  former 
case  the  'anterior'  end  may  be  directed  'positively,'  toward  the  source  of 
stimulation,  or  'negatively,'  away  from  it.  It  now  appears  a  matter  of 
course  that  if  forward  motion  takes  place  after  such  orientation,  its 
direction  will  correspond  to  the  direction  of  the  stimulus"  (Driesch, 
1903,  p.  5,  translation). 

(2)  This  orientation  is  produced,  according  to  this  tropism  theory, 
by  the  direct  action  of  the  stimulating  agent  on  the  motor  organs  of  that 
side  of  the  body  on  which  it  impinges.  A  stimulus  striking  one  side  of 
the  body  causes  the  motor  organs  of  that  side  to  contract  or  extend  or 
to  move  more  or  less  strongly.  This,  of  course,  turns  the  body,  till  the 
stimulus  affects  both  sides  equally ;  then  there  is  no  occasion  for  further 
turning,  and  the  animal  is  oriented.  "These  tropisms  are  identical 
for  animals  and  plants.  The  explanation  of  them  depends  first  on  the 
specific  irritability  of  certain  elements  of  the  body  surface,  and,  second, 
upon  the  relations  of  symmetry  of  the  body.  Symmetrical  elements  at 
the  surface  of  the  body  have  the  same  irritability;  unsymmetrical  ele- 
ments have  a  different  irritability.  Those  nearer  the  oral  pole  possess 
an  irritability  greater  than  that  of  those  near  the  aboral  pole.  These 
circumstances  force  an  animal  to  orient  itself  toward  a  source  of  stimu- 
lation in  such  a  way  that  symmetrical  points  on  the  surface  of  the  body 
are  stimulated  equally.  In  this  way  the  animals  are  led  without  will  of 
their  own  either  toward  the  source  of  stimulus  or  away  from  it"  (Loeb, 
1900,  p.  7).  Holt  and  Lee  (1901,  pp.  479-480)  bring  out  this  point  in 
the  prevailing  theory,  as  applied  to  light,  as  follows :  "The  light  operates, 
naturally,  on  the  part  of  the  animal  which  it  reaches.  The  intensity  of 
the  light  determines  the  sense  of  the  response  whether  contractile  or 
expansive,  and  the  place  of  the  response,  the  part  of  the  body  stimulated, 
determines  the  ultimate  orientation  of  the  animal." 

How  the  orientation  is  brought  about  according  to  this  theory  may 


THE   TROPISM   THEORY 


267 


be  illustrated  most  simply  by  considering  an  organism  covered  with 
cilia.  For  this  purpose  we  may  employ  the  accompanying  diagrams, 
based  on  those  given  by  Verworn  (1895,  p.  484),  but  modified  to  make 
them  clearer.     In  Fig.  142  a  stimulus  is  supposed  to  act  from  the  right 


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side  on  the  organism,  as  indicated  by  the  arrows,  and  to  cause  the  cilia 
of  that  side  to  contract  more  strongly,  as  is  indicated  by  the  heavier 
shade  and  greater  curving.  This  must,  of  course,  turn  the  body  to  the 
left,  as  a  boat  is  turned  to  the  left  when  the  right  oar  is  more  strongly 


268  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

pulled.  The  animal  therefore  occupies  successively  the  positions  1,2,3, 
and  4.  In  the  position  4  both  sides  are  equally  affected  by  the  stimulus, 
so  that  there  is  no  cause  for  further  turning.  The  animal  has  become 
oriented  and  its  usual  forward  movements  now  take  it  away  from  the 
source  of  stimulation.  We  have  here  a  case  of  negative  tropism  or 
taxis. 

Figure  143  illustrates  the  conditions  producing  positive  tropism  or 
taxis.  The  stimulus,  coming  from  the  right  side,  is  supposed  to  cause 
the  cilia  of  that  side  to  beat  less  strongly  backward,  or  to  beat  forward. 
As  a  result  the  organism  is  turned  to  the  right,  through  the  positions 
1,  2,  3,  4,  till  its  anterior  end  is  directed  toward  the  source  of  stimulation. 
Both  sides  are  now  affected  alike,  and  there  is  no  cause  for  further  turn- 
ing. The  animal  now  moving  forward  in  the  usual  way  of  course  travels 
toward  the  source  of  stimulation. 

As  an  example  of  the  application  of  the  tropism  scheme  to  a  mus- 
cular organism,  we  may  take  Davenport's  exposition  of  the  action  of 
light  in  determining  the  direction  of  locomotion  of  the  earthworm. 
"Represent  the  worm  by  an  arrow  whose  head  indicates  the  head  end 
(Fig.  144,  A ).  Let  solar  rays  SS  fall  upon  it  horizontally  and  perpendicu- 
larly to  its  axis.  Then  the  impinging  ray  strikes  it  laterally,  or,  in  other 
words,  it  is  illuminated  on  one  side  and  not  on  the  other.  Since,  now, 
the  protoplasm  of  both  sides  is  attuned  to  an  equal  intensity  of  light, 

that  which  is  the  less 
S  illuminated  is  nearer  its 
optimum  intensity.  Its 
protoplasm  is  in  a  photO- 
Low  light  attuncment  tonic       conclition.  That 

■A    "        T      ,.  ,  „    .,  .  '  which  is  strongly  illumin- 

Low  light  attunement  o  J 

■c  -..  ,  .  ated  has  lost  its  phototonic 

Fig.  144.  —  Diagram  to  explain  a  tropism  in  a  muscu-  _  |  r 

lar  organism,  such  as  the  earthworm.     After  Davenport,    condition.      Only  the  dark- 

See  text*  ened    muscles,    then,    are 

capable  of  normal  contraction;  the  brightly  illuminated  ones  are  re- 
laxed. Under  these  conditions  the  organism  curves  toward  the  darker 
side;  and  since  its  head  region  is  the  most  sensitive,  response  begins 
there.  Owing  to  a  continuance  of  the  causes,  the  organism  will  con- 
tinue to  turn  from  the  light  until  both  sides  are  equally  illuminated, 
i.e.  until  it  is  in  the  light  ray.  Subsequent  locomotion  will  carry  the 
organism  in  a  straight  line,  since  the  muscles  of  the  two  sides  now  act 
similarly.  Thus  orientation  of  the  organism  is  effected.  The  same 
explanation,  which  is  modified  from  one  of  Loeb  ('93,  p.  86),  will  ac- 
count, mutatis  mutandis,  for  positive  phototaxis "  (Davenport,  1897, 
p.  209). 


THE   TROPISM   THEORY  269 

From  the  relations  above  set  forth,  it  follows  that  for  determination 
of  the  direction  of  movement  in  accordance  with  this  tropism  theory, 
a  stimulus  must  act  upon  one  portion  of  the  body  differently  from  or 
more  intensely  than  on  other  parts.  Without  such  differential  action 
on  different  parts  of  the  body  there  is  nothing  to  cause  the  animal  to 
turn  in  one  direction  or  another. 

This  tropism  schema  is  made  by  its  upholders  the  basis  for  the 
larger  part  of  the  directed  activities  of  the  lower  animals.  "Thus  the 
phenomena  of  positive  and  negative  chemotaxis,  thermotaxis,  photo- 
taxis,  and  galvanotaxis,  which  are  so  highly  interesting  and  important 
in  all  organic  life,  follow  with  mechanical  necessity  as  the  simple  results 
of  differences  in  biotonus,  which  are  produced  by  the  action  of  stimuli 
at  two  different  poles  of  the  free-living  cell"  (Verworn,  1899,  p.  503). 
Verworn  (1899)  and  Loeb  (1900)  have  developed  the  theory  as  a  general 
explanation  for  all  sorts  of  directed  activities,  and  many  authors  have 
accepted  it  for  reactions  to  particular  stimuli.  In  recent  times,  Holt 
and  Lee  (1901)  have  applied  it  in  detail  to  the  responses  to  light,  Loeb 
(1900,  p.  186)  and  Garrey  (1900)  to  chemicals,  Loeb  (1897)  and  Verworn 
(1899)  to  gravitation,  Mendelssohn  (1902  a)  to  heat  and  cold. 

In  the  foregoing  chapters  we  have  examined  the  behavior  of  a  con- 
siderable number  of  lower  organisms,  of  many  different  kinds.  How 
far  does  this  examination  support  the  above  theory?  How  far  is  the 
observed  behavior  due  to  orientation  produced  by  the  local  action  of 
stimuli  on  the  different  parts  of  the  body?  To  what  extent  does  this 
tropism  theory  aid  us  in  understanding  the  behavior  of  these  organisms  ? 

In  Amoeba  there  are  no  permanent  body  axes ;  anterior  and  posterior 
ends  continually  interchange  places  in  the  rolling  movement,  and  any 
part  may  become  at  any  time  the  advancing  portion.  Under  these 
conditions  the  term  "orientation"  can  have  little  meaning,  and  we  can 
hardly  say  that  stimulation  causes  the  body  to  become  oriented  in  a 
certain  way.  But  stimulation  does  determine  the  direction  of  motion, 
and  anything  like  orientation  that  can  be  distinguished  is  a  result  of  the 
direction  of  motion,  not  its  cause.  Under  stimulation  the  direction  of 
movement  is  changed  first,  then  in  consequence  the  animal  takes  an 
elongated  form  which  furnishes  the  only  possible  basis  for  the  use  of  the 
term  "orientation." 

In  the  fact  that  to  produce  directed  movement,  local  action  of  the 
stimulus  on  a  certain  part  of  the  body  is  necessary,  causing  local  contrac- 
tion or  extension,  the  conditions  in  Amceba  agree  with  the  fundamental 
postulates  of  the  tropism  theory.  The  agreement  is  most  precise  in  the 
positive  reactions,  where  the  part  stimulated  is  the  part  that  extends 
and  determines  the  direction  of  movement.     In  the  negative  reactions 


270  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

the  agreement  with  the  theory  is  less  complete ;  for  while  the  part  that 
contracts  is  determined  by  the  region  stimulated,  the  extension  and 
consequent  direction  of  movement  are,  as  a  rule,  not  thus  determined. 

But  while  some  important  features  of  the  behavior  of  Amoeba  are 
thus  in  agreement  with  the  underlying  assumptions  of  the  tropism 
theory,  it  is  certain  that  for  such  organisms  alone  the  theory  would  never 
have  been  proposed.  The  facts  for  Amoeba  can  be  formulated  in  a 
much  simpler  way  than  by  bringing  in  the  conception  of  orientation,  — 
a  conception  derived  from  organisms  with  permanent  body  axes,  and 
fitting  only  these. 

But  when  we  turn  to  an  examination  of  the  behavior  of  those  uni- 
cellular organisms  having  permanent  body  axes,  we  find  the  conditions 
widely  at  variance  with  the  assumptions  of  the  local  action  tropism 
theory.  In  the  infusoria  most  of  the  behavior  is  quite  inconsistent  with 
the  theory.  The  reactions  are  not  determined  by  the  direct  action  of 
a  localized  stimulus  in  producing  greater  contraction  or  extension  in 
that  part  of  the  body  on  which  it  impinges.  The  organism  responds 
as  a  whole,  by  a  reaction  involving  all  parts  of  the  body.  It  does  not 
necessarily  turn  directly  toward  or  directly  away  from  the  source  of 
stimulation,  as  would  be  the  case  if  it  reacted  in  accordance  with  this 
tropism  theory.  The  direction  of  turning  is  determined  by  internal 
factors;  the  animal  turns  toward  a  side  which  is  structurally  defined. 
For  inducing  directed  motion  it  is  not  necessary  that  the  stimulus  should 
act  differently  on  different  parts  of  the  body.  The  cause  of  reaction  — 
that  is,  of  a  change  in  the  movements  —  is  usually  a  change  from  one 
condition  or  intensity  to  another.  Thus  the  essential  point  in  deter- 
mining whether  reaction  shall  occur  is  in  most  cases  the  direction  of 
movement  —  whether  this  takes  the  organism  (or  its  most  sensitive 
portion)  away  from,  or  toward,  the  optimum.  It  is  difficult  to  conceive 
a  type  of  behavior  more  completely  opposed  to  the  local  action  theory 
of  tropisms  above  set  forth. 

In  some  cases  this  method  of  reaction  produces  orientation  with 
relation  to  the  direction  of  some  external  force,  in  other  cases  it  does  not. 
The  orientation  when  it  occurs  is  brought  about  through  continued 
movements  that  are  varied  in  direction,  with  final  selection  of  one  of 
these  directions.  Whether  orientation  shall  or  shall  not  result  depends 
on  whether  it  must  result  in  order  that  there  shall  be  a  cessation  of  the 
stimulation  which  is  producing  the  varied  movements.  These  relations 
have  been  set  forth  in  detail  in  our  account  of  the  behavior  of  Paramecium 
(Chapter  IV,  Section  6),  so  that  it  is  not  necessary  to  take  them  up  here. 

To  almost  all  the  relations  set  forth  in  the  preceding  paragraphs 
there  is  one  exception.     In  the  reaction  of  ciliate  infusoria  to  the  electric 


THE   TROPISM   THEORY  271 

current  we  find  certain  features  which  agree  with  the  local  action  tropism 
theory.  These  features  are  so  striking  and  so  utterly  at  variance  with 
everything  found  in  the  remainder  of  the  behavior  of  these  organisms 
that  they  throw  into  strong  relief  the  contrast  between  the  usual  behavior 
and  the  requirements  of  this  tropism  schema.  Owing  to  the  remarkable 
cathodic  reversal  of  the  cilia  (a  phenomenon  not  paralleled  under  any 
other  conditions),  the  motor  organs  of  opposite  sides  or  ends  of  the 
ciliate  infusorian  act  under  the  electric  current  in  different  ways.  The 
result  is  behavior  partly  in  accordance  with  the  tropism  schema.  This 
furnishes  us  with  a  picture  of  what  behavior  would  be  if  this  schema 
held  throughout.  The  unity  and  coordination  that  are  so  striking  in 
the  remainder  of  the  behavior  are  here  quite  lost.  Different  parts  of 
the  motor  organs  urge  the  organism  in  different  directions  at  the  same 
time.  The  animal  seems  to  be  trying  to  do  two  opposed  things  at  once 
(see  p.  89).  Nothing  more  ineffective  and  unpurposive  can  be  imag- 
ined than  such  behavior.  But  in  producing  these  local  effects  the  elec- 
tric current  is  unique  among  stimuli,  and  the  reaction  is  as  far  from 
the  typical  behavior  of  these  organisms  as  can  be  imagined.  The  elec- 
tric current  may  be  used  for  producing  local  contractions  in  man  as 
well  as  in  Paramecium,  but  such  contractions  cannot  be  considered  an 
adequate  type  of  the  behavior  of  mankind.  The  electric  current  never 
acts  effectively  on  the  organisms  under  the  natural  conditions,  so  that 
normally  they  never  show  the  peculiar  behavior  produced  by  it.  To 
all  the  natural  conditions  of  existence  they  react  in  a  totally  different 
manner  —  a  manner  quite  at  variance  with  this  tropism  schema. 

In  the  bacteria  as  in  the  infusoria  the  behavior  is  not  in  accordance 
with  the  above-discussed  theory  of  tropisms.  The  details  of  the  re- 
actions are  not  so  completely  known  as  in  the  infusoria.  But  what  we 
know  shows  that  the  behavior  of  these  organisms  so  far  as  involved  in 
the  directed  reactions  is  as  follows:  When  stimulated  the  bacterium 
changes  its  course,  moving  in  some  other  direction,  —  a  direction  de- 
termined by  its  own  body  structure,  and  not  by  the  position  of  the 
stimulating  agent. 

Thus  we  find  in  the  unicellular  organisms  very  little  in  the  behavior 
that  can  be  interpreted  in  accordance  with  this  local  action  theory  of 
tropisms.  The  latter  does  not  by  any  means  express  the  fundamental 
nature  of  their  behavior  in  directed  reactions.  These  are  based  chiefly 
on  the  performance  under  stimulation  of  varied  movements,  with  selec- 
tion from  the  resulting  conditions,  —  the  "method  of  trial." 

In  the  symmetrical  Metazoa  we  of  course  find  many  cases  in  which 
the  animal  turns  directly  toward  or  away  from  a  source  of  stimulation, 
without  anything  in  the  nature  of  preliminary  trial  movements.     This 


272  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

is  a  simple  fact  of  observation,  which  leaves  open  the  possibility  of  many 
different  explanations.  Is  the  simple  explanation  given  by  the  local 
action  theory  of  tropisms  one  that  is  of  general  applicability  to  the 
directed  reactions  of  lower  and  higher  Metazoa  ? 

In  considering  the  evidence  on  this  question,  we  find  that  even  in 
symmetrical  Metazoa  the  direction  of  movement  with  reference  to  ex- 
ternal agents  is  by  no  means  always  brought  about  by  a  simple,  direct 
turning.  On  the  contrary,  in  many  of  the  Metazoa,  trial  movements  are 
as  noticeable  and  important  as  in  the  Protozoa.  This  we  have  illustrated 
in  detail  for  many  invertebrates  in  the  section  devoted  to  this  subject 
(Chapter  XII,  Section  2).  For  such  behavior  the  local  action  theory 
of  tropisms  fails  to  give  determining  factors. 

In  some  cases  the  turning  movements  are  directly  toward  or  from 
certain  stimuli.  But  the  question  here  is,  whether  this  turning  is  pro- 
duced by  the  local  action  of  the  agent  in  question  on  the  part  of  the 
body  against  which  it  impinges,  as  is  asserted  by  the  theory  which  we 
are  considering,  and  illustrated  in  Fig.  144. 

In  a  few  instances  this  is  apparently  the  case.  The  medusa  escapes 
unfavorable  stimulation  by  contracting  most  strongly  on  the  side  on 
which  the  stimulus  impinges.  In  Hydra  local  stimulation  by  chemicals, 
heat,  or  electricity  often  produces  limited  local  contraction,  causing  the 
animal  to  bend  toward  the  side  stimulated.  In  various  sea  anemones 
the  tentacles,  and  sometimes  the  body,  may  bend  toward  the  side  stimu- 
lated, as  this  theory  demands.  Yet  this  direct  contraction  plays  very 
little  part  in  the  behavior  of  these  animals.  In  Hydra  it  is  only  injurious 
agents  to  which  the  animal  responds  in  this  way,  and  the  result  is  to  still 
further  subject  the  animal  to  the  action  of  the  injurious  agent.  In  order 
to  escape  the  action  of  injurious  stimuli,  Hydra  has  recourse  to  behavior 
of  quite  a  different  character,  and  in  its  natural  life  there  seems  to  be 
no  indication  that  behavior  ever  occurs  in  accordance  with  this  theory 
of  direct  local  action.  In  sea  anemones  the  direct  turning  toward  the 
region  stimulated  is  at  once  supplemented  by  movements  determined  in 
quite  a  different  way,  —  through  the  structure  of  the  organism,  —  the 
tentacles  bending  toward  the  mouth.  Without  this  supplementary  re- 
action the  local  bending  would  be  of  no  service.  In  the  hydroid  Cory- 
morpha  it  is  only  this  second  method  of  bending  that  occurs  at  all. 
Throughout  the  Ccelenterata  the  part  played  by  trial  movements,  not 
directly  determined  by  the  position  of  the  stimulating  agent,  is  most 
striking  and  important. 

In  the  echinoderms  we  have,  as  in  Amoeba,  organisms  which  are 
as  a  rule  without  a  definite  body  axis,  so  far  as  the  direction  of  locomo- 
tion goes;    there  is  usually  no  permanent  anterior,  posterior,  right,  or 


THE   TROPISM   THEORY  273 

left.  Hence  a  theory  like  that  of  tropisms,  based  primarily  on  the  posi- 
tion or  orientation  of  the  body  axis  with  reference  to  the  direction  of 
the  stimulating  agent,  can  find  little  precise  application.  Yet  it  is  again 
in  this  group  that  we  find  behavior  that  is  in  certain  respects  at  least  in 
accordance  with  the  tropism  theory.  For  locomotion  in  a  certain  direc- 
tion the  stimulus  must  be  localized,  acting  in  a  different  way  on  the  two 
sides;  this  is  one  of  the  postulates  of  the  tropism  theory.  Further,  a 
local  stimulation  may  have  at  least  a  partially  local  effect,  and  this  may 
result  in  movement  in  a  certain  direction.  But  as  v.  Uexkull  has  well 
pointed  out,  the  elementary  factors  here  are  the  typical  reaction  methods 
(" reflexes")  of  the  individual  organs  of  the  body  surface.  The  tropism, 
if  we  attempt  to  apply  the  concept  at  all,  is  a  mere  collection  of  these 
elementary  reactions ;  it  is  not  in  any  sense  itself  an  elementary  factor. 
In  other  words,  the  tropism  theory  would  never  have  been  based  on  the 
known  behavior  of  the  echinoderms,  for  the  facts,  even  so  far  as  they 
agree  with  the  fundamental  postulates  of  the  theory,  can  be  formulated 
more  directly  and  simply  in  another  way.  The  tropism  theory  is  fur- 
nished with  an  apparatus  of  relations  that  finds  no  application  to  the 
starfish  and  sea  urchin. 

Furthermore,  as  we  have  shown  in  detail,  much  of  the  behavior  of 
these  animals  is  based  on  the  method  of  trial.  In  such  bilaterally  sym- 
metrical animals  as  the  flatworm  Planaria  we  have  the  most  favorable 
possible  conditions  for  action  on  this  tropism  theory,  and  such  animals 
often  do  turn  directly  toward  or  away  from  sources  of  stimulation.  But 
when  this  occurs,  is  it  due  merely  to  the  local  contraction  or  extension 
of  the  musculature  on  the  side  on  which  the  stimulus  impinges,  or  is  it 
a  reaction  of  the  animal  as  a  whole  ? 

This  question  can  be  answered  only  by  a  thorough  study  of  all  the 
factors  in  the  reaction;  such  a  study  is  given  us  for  the  flatworm  by 
Pearl  (1903).  The  positive  reaction  of  the  flatworm  —  the  direct  turn- 
ing toward  the  source  of  stimulation  —  seem  to  present  ideal  condi- 
tions for  explanation  on  the  simple  tropism  theory.  But  Pearl,  after 
exhaustive  study,  concludes  that  the  processes  in  the  reaction  are  as 
follows :  — 

"A  light  stimulus,  when  the  organism  is  in  a  certain  definite  tonic 
condition,  sets  off  a  reaction  involving  (1)  an  equal  bilateral  contraction 
of  the  circular  musculature,  producing  the  extension  of  the  body;  (2)  a 
contraction  of  the  longitudinal  musculature  of  the  side  stimulated,  pro- 
ducing the  turning  toward  the  stimulus  (this  is  the  definitive  part  of  the 
reaction);  and  (3)  contraction  of  the  dorsal  longitudinal  musculature, 
producing  the  raising  of  the  anterior  end.  In  this  reaction  the  sides  do 
not  act  independently,  but  there  is  a  delicately  balanced  and  finely  co- 


274  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

ordinated  reaction  of  the  organism  as  a  whole,  depending  for  its  existence 
on  an  entirely  normal  physiological  condition"  (Pearl,  1903,  p.  619). 

Similar  lack  of  uniformity  and  simplicity  appears  in  the  remainder 
of  the  behavior  of  the  flatworm.  In  few  of  the  lower  metazoa  has  the 
movement  been  so  thoroughly  analyzed  as  in  Planaria.  But  there  seems 
to  be  no  reason  for  thinking  that  in  this  simple  animal  these  relations  are 
more  complex  than  in  most  invertebrates. 

The  recent  thorough  studies  of  Radl  (1903)  on  reactions  to  light  in 
many  animals  have  shown  clearly  the  inadequacy  of  this  theory  to  ac- 
count for  most  of  the  reactions  to  this  agent.  Bohn  (1905)  has  likewise 
been  compelled  to  reject  this  theory,  on  the  basis  of  the  results  of  his 
thorough  studies  on  the  behavior  of  the  animals  of  the  seashore.  To 
the  writer  it  appears  that  most  of  the  recent  thorough  work  on  animal 
behavior  points  in  the  same  direction. 

We  must  then  conclude  from  our  examination  of  the  facts  that  for 
the  lower  organisms  taken  into  consideration  in  the  present  work,  the 
local  action  theory  of  tropisms  is  of  comparatively  little  value  for  inter- 
preting behavior.  This  theory  uses  and  attempts  to  make  of  general 
application  certain  elements  here  and  there  observable  in  the  behavior 
of  some  organisms.  But  in  many  organisms  even  these  elements  are 
almost  completely  lacking,  and  in  no  organism  that  we  have  taken  up 
does  this  theory  adequately  express  the  nature  of  behavior.  The  tro- 
pism  as  applied  to  animal  behavior  in  the  sense  we  have  considered,  is 
not  an  elementary  factor ;  it  is  only  a  more  or  less  artificial  construction, 
made  by  combining  certain  elements  of  behavior  and  omitting  others 
that  are  of  most  essential  significance.  It  makes  use  of  certain  simple 
phenomena  that  actually  exist,  but  elevates  these  into  a  general  explana- 
tion of  directed  behavior,  for  which  they  are  utterly  inadequate.  The 
prevalence  of  this  local  action  theory  of  tropisms  as  a  general  explana- 
tion of  behavior  in  lower  organisms  is  based  only  on  an  incomplete  knowl- 
edge and  an  insufficient  analysis  of  the  facts  of  behavior. 

Other  Terms  employed  in  Accounts  of  Animal  Behavior 

In  the  foregoing  pages  we  have  criticised  a  certain  definite  theory  of 
tropisms,  this  being  the  theory  most  commonly  implied  when  the  word 
is  used  in  a  precisely  defined  way.  But  the  term  "tropism"  is  often 
used  in  a  looser  sense.  By  some  writers  the  word  is  applied  merely  to 
the  general  phenomenon  that  the  movements  of  organisms  show  definite 
relations  to  the  location  of  external  agents.  In  this  sense  the  word  im- 
plies no  theory,  and  is  not  open  to  criticism  on  the  basis  of  observed 
facts.     It  is,  of  course,  equally  applicable  to  the  behavior  of  man  and 


THE   TROPISM    THEORY  275 

that  of  lower  organisms;  in  this  sense  the  botanist  Pfeffer  (1904,  p.  587) 
consistently  remarks  that  a  man  who  bends  toward  a  lighted  window 
shows  phototropism  as  does  a  plant.  The  use  of  the  word  in  this  purely- 
descriptive  sense  is  often  convenient,  but  we  need  to  keep  in  mind  the 
fact  that  the  word  thus  used  involves  no  explanation,  and  includes  phe- 
nomena of  the  most  heterogeneous  character. 

By  some  writers  the  word  "  tropism  "  is  restricted  to  the  bending  or 
inclination  of  a  fixed  organism,  while  the  movements  of  free  organisms 
under  the  influence  of  external  agents  are  called  taxis.  This  distinc- 
tion is  a  purely  descriptive  one. 

Some  writers  reserve  the  term  "  tropism  "  (or  taxis)  for  those  reactions 
in  which  the  organism  takes  up  a  well-defined  orientation  with  relation 
to  the  line  of  action  of  some  external  agent.  Other  reactions,  in  which 
orientation  is  not  a  feature,  are  variously  designated  as  kinesis  (Engel- 
mann,  1882  a;  Rothert,  1901 ;  Garrey,  1900),  as  -pathy  (Davenport, 
1897;  Yerkes,  1903  b;  and  others),  as  -metry  (Strasburger,  1878;  Olt- 
manns,  1892),  and  by  various  other  names,  depending  on  the  method 
by  which  the  author  in  question  considers  them  to  be  brought  about. 
On  this  basis  the  reactions  of  infusoria  to  water  currents,  gravity,  the 
electric  current,  and  to  light  coming  from  one  side  would  be  called 
tropisms  or  taxis;  while  the  reactions  to  chemicals,  osmotic  pressure, 
heat  and  cold,  and  mechanical  stimuli  would  be  designated  by  some 
other  term. 

An  immense  number  of  technical  terms  have  been  devised  for  appli- 
cation to  the  phenomena  of  behavior  in  the  lower  organisms.  A  system- 
atic exposition  of  a  very  complete  set  of  such  terms  will  be  found  in  the 
paper  of  Massart  (1901).  The  "Plant  Physiology"  of  Pfeffer  (1904) 
likewise  deals  extensively  with  this  matter.  A  proposed  new  terminol- 
ogy applying  to  many  of  the  features  of  behavior  is  set  forth  by  Beer, 
Bethe,  and  v.  Uexkull  (1899).  A  number  of  other  references  to  this 
matter  will  be  found  in  the  literature  list  at  the  end  of  the  present  chapter. 

As  to  the  value  of  giving  technical  names  to  every  distinguishable  act 
that  an  organism  performs,  opinions  will  differ.  So  far  as  the  names 
are  purely  descriptive,  expressing  nothing  more  than  some  observed 
action  of  the  organism,  it  is  difficult  to  see  any  very  great  advantage  in 
their  use.  To  say  that  an  organism  shows  phobism  (Massart),  is  merely 
to  say  that  it  moves  backward;  to  say  that  it  reacts  by  dorsoclinism 
(Massart),  is  the  same  as  to  say  that  it  reacts  by  turning  toward  the  dorsal 
side.  To  most  readers  the  latter  expressions  are  more  intelligible  than 
the  former,  and  they  are  equally  accurate  and  complete.  Such  purely 
descriptive  terms  embody  no  results  of  scientific  analysis.  Their  use  is 
therefore  merely  a  question  of  convenience  or  taste  on  the  part  of  the 


276  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

writer.     They  are  doubtless  at  times  convenient  and  may  perhaps  be 
used  to  advantage. 

So  far  as  the  terms  involve  a  certain  explanation  of  the  phenomena, 
their  use  requires  that  the  writer  shall  accept  that  explanation  for  the 
phenomena  in  question,  otherwise  their  use  gives  rise  to  misconception. 
This  makes  many  of  the  terms  unavailable,  save  in  a  very  restricted 
degree.  The  study  of  behavior  seems  hardly  to  have  reached  as  yet 
the  stage  where  a  hard  and  fast  nomenclature  can  be  used  to  advantage. 
To  the  present  writer,  after  a  long- continued  attempt  to  use  some  of  the 
systems  of  nomenclature  devised,  descriptions  of  the  facts  of  behavior  in 
the  simplest  language  possible  seems  a  great  gain  for  clear  thinking  and 
unambiguous  expression.  If  investigators  on  the  lower  organisms  would 
for  a  considerable  time  devote  themselves  to  giving  in  such  simple  terms 
a  full  account  of  behavior  in  all  its  details,  paying  special  attention  to 
the  effect  of  the  movements  performed  on  the  relation  of  the  organism 
to  the  stimulating  agent,  this  would  be  a  great  gain  for  our  understanding 
of  the  real  nature  of  behavior,  and  some  theories  now  maintained  would 
quickly  disappear.  Less  attention  to  nomenclature  and  definitions,  and 
more  to  the  study  of  organisms  as  units,  in  their  relation  to  the  environ- 
ment, is  at  the  present  time  the  great  need  in  the  study  of  behavior  in 
lower  organisms. 

LITERATURE  XIV 

A.  The  local  action  theory  of  tropisms :  Loeb,  1900,  1897;  Verworn,  1895, 
1899;  Davenport,  1897  ;  Driesch,  1903  ;  Radl,  1903  ;  Holt  and  Lee,  1901 ;  Men- 
delssohn, 1902  a;  Garrey,  1900;  Bohn,  1905  ;  Jennings,  1904  c. 

B.  Nomenclature  and  classification  in  behavior  :  Pfeffer,  1904  ;  Massart,  1901  ; 
Beer,  Bethe,  and  v.  Uexkull,  1899;  Nagel,  1899;  Claparede,  1905  ;  Haber- 
landt,  i905;  zlegler,  i900  ;  nuel,  i904  ;  davenport,  1 897  ;  pvothert,  i90i  ; 
Engelmann,  1882  a;  Loeb,  1893,  1900;  Garrey,  1900;  Strasburger,  1878; 
Oltmanns,  1892;  Yerk.es,  1903  b. 


CHAPTER   XV 

IS   THE    BEHAVIOR    OF   THE    LOWER    ORGANISMS    COMPOSED  OF 

REFLEXES? 

The  simplest  reaction  of  an  organism  is  the  performance  of  a  definite 
simple  act  in  response  to  a  definite  stimulus.  Such  is  the  contraction  of 
Vorticella,  such  the  reversal  of  movement  in  a  bacterium  or  in  Para- 
mecium or  the  flatworm.  A  simple  responsive  action  of  this  sort  is 
commonly  known  as  a  reflex.  The  question  has  been  raised  as  to 
whether  the  behavior  of  the  lower  organisms  differs  from  that  of  higher 
animals  in  being  purely  reflex  or  not ;  in  other  words,  whether  all  their 
reactions  to  stimuli  are  reflexes.  For  various  organisms  this  question  is 
answered  by  many  authors  in  the  affirmative.  In  some  cases  the  be- 
havior of  animals  much  higher  in  the  scale  than  most  of  those  we  have 
considered  is  characterized  as  purely  reflex.  This  is  v.  Uexkull's  view 
for  the  sea  urchin.  We  must  examine  briefly  the  question  whether 
behavior  in  these  lowest  organisms  is  properly  characterized  as  reflex. 

What  is  "a  reflex?  The  concept  of  reflex  action  has  had  a  complex 
origin,  and  as  a  result  it  is  defined  in  various  ways.  One  of  the  phe- 
nomena on  which  the  concept  is  based  is  the  contraction  of  a  muscle 
when  a  certain  nerve  is  stimulated.  The  stimulation  is  supposed  to  pass 
from  the  nerve  to  the  spinal  cord,  whence  it  is  reflected  back  to  the  mus- 
cle; hence  the  name  reflex.  Some  authors  hold  that  the  term  can  be 
properly  used  only  of  acts  thus  performed  by  the  aid  of  the  nervous 
system.  This  would  of  course  exclude  reflexes  from  the  behavior  of 
unicellular  organisms,  and  introduce  uncertainty  in  dealing  with  the 
lower  Metazoa,  for  in  many  of  these  we  do  not  know  whether  the  re- 
actions are  throughout  mediated  by  the  nervous  system  or  not.  But  it 
is  more  usual  to  consider  the  reflex  as  a  certain  type  of  action,  without 
regard  to  the  particular  anatomical  structures  involved.  Even  where 
the  term  is  limited  to  actions  produced  through  the  nervous  system,  some 
other  term  is  employed  to  indicate  the  corresponding  type  of  action  in 
animals  without  a  nervous  system,  so  that  the  existence  of  a  particular 
kind  of  action,  indicated  usually  by  the  word  "  reflex,"  is  recognized. 
Thus,  Beer,  Bethe,  and  v.  Uexkull  (1899)  use  for  reflexes  performed 
without  a  nervous  system  the   word   "antitype."      We   may  then   ex- 

277 


278  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

amine  the  reflex  (or  antitype)  simply  as  a  type  of  action,  without  regard 
to  the  existence  of  a  nervous  system. 

A  second  phenomenon  on  which  the  concept  of  reflex  action  is  based 
is  the  following :  In  ourselves,  certain  acts  are  performed  unconsciously. 
These  acts  have  been  considered  identical  with  those  due  to  the  passage 
of  an  impulse  from  the  nerve-ending  to  the  spinal  cord,  and  thence  back 
to  the  muscle ;  that  is  with  reflexes.  Hence  the  reflex  is  often  defined 
as  an  unconscious  or  involuntary  action  :  "  Such  involuntary  responses  we 
know  as  'reflex'  acts"  (James,  "Psychology,"  Vol.  I,  p.  13).  "Reflexes 
are  voluntary  acts  that  have  become  mechanical"  (Wundt).  This  defi- 
nition of  a  reflex  act  as  involuntary  or  unconscious  is  widely  employed. 
If  we  accept  this  definition,  there  is  of  course  no  way  by  which  we  can 
tell  whether  the  reactions  of  lower  animals  are  reflex  or  not.  By  obser- 
vation we  cannot  tell  whether  the  reacting  organism  is  conscious,  for 
this  would  require,  as  Titchener  (1902)  says,  an  objective  criterion  of 
the  subjective,  —  an  objective  criterion  of  that  which  is  not  objective, 
and  this  is  impossible.  It  is  certainly  as  dogmatic  and  unscientific  to 
assert  that  the  actions  of  organisms  are  reflex  in  the  sense  of  uncon- 
scious, as  to  assert  the  opposite,  for  we  have  no  knowledge  on  this 
point.  We  can  recognize  reflex  acts,  from  this  point  of  view,  only  in 
ourselves. 

A  third  phenomenon  on  which  the  conception  of  a  reflex  is  based  is 
the  supposed  uniformity  of  certain  reactions.  The  muscle  responds  to 
all  sorts  of  stimuli  by  contracting.  This  uniformity  is  considered  by 
many  authors  the  essential  feature  in  reflexes.  Hobhouse  (1901,  pp.  28, 
29)  defines  reflexes  as  "uniform  responses  to  simple  stimuli."  Accord- 
ing to  Beer,  Bethe,  and  v.  Uexkiill  (1899,  p.  3),  reflexes  are  reactions 
"always  recurring  in  the  same  manner."  Driesch  (1903)  says  a  reflex 
is  "a  motor  reaction  which  as  a  response  to  a  stimulus  occurs  the  first 
time  completely  and  securely." 

This  objective  definition  of  a  reflex  as  an  invariable  reaction  to  a 
simple  stimulus  is  the  only  one  which  we  can  really  use  in  determining 
by  means  of  objective  study  whether  the  behavior  of  animals  is  reflex 
in  character.  Is  the  behavior  of  lower  organisms  composed  of  reflexes 
in  this  sense? 

Possibly  the  best  case  for  an  affirmative  answer  to  this  question  could 
be  made  out  for  the  bacteria.  Here  there  is  so  far  as  known  only  one 
form  of  motor  reaction,  —  the  reversal  of  movement  when  stimulated. 
But  even  in  the  bacterium  the  uniformity  is  disturbed  by  the  fact  that 
on  coming  in  contact  with  a  solid  the  organism  sometimes  comes  to  rest 
against  it,  while  at  other  times  it  reacts  by  the  reversal  of  motion.  Owing 
to  their  minuteness,  the  behavior  of  these  organisms  is  less  known  than 


REFLEXES  IN  BEHAVIOR  279 

that  of  other  unicellular  forms,  so  that  it  is  difficult  to  make  a  positive 
generalization  on  such  a  point  as  the  present  one. 

If  we  attempt  to  apply  our  definition  of  a  reflex  to  the  behavior  of 
the  infusoria,  —  of  Paramecium,  for  example,  —  we  at  once  get  into 
difficulties.  The  "avoiding  reaction"  of  Paramecium  is  sharply  limited 
in  many  ways,  and  always  takes  place  in  accordance  with  a  definite  type. 
But  it  is  far  from  being  invariable.  The  reaction  is  composed  of  three 
factors,  which  may  vary  more  or  less  independently  of  each  other,  in 
such  a  way  that  an  absolutely  unlimited  number  of  combinations  may 
result,  all  fitting  the  generalized  type.  The  possible  variations  may  be 
summed  up  as  follows :  If  the  animal  be  taken  as  a  centre  about  which 
a  sphere  is  described,  with  a  radius  several  times  the  length  of  the  body, 
then  as  a  result  of  the  avoiding  reaction  the  animal  may  traverse  the 
peripheral  surface  of  this  sphere  at  any  point,  moving  at  the  time  either 
backward  or  forward.  In  other  words,  the  reaction  may  carry  it  in  any 
one  of  the  unlimited  number  of  directions  leading  from  its  position  as  a 
centre.  While  the  direction  of  turning  is  absolutely  defined  by  the  struc- 
ture of  the  animal,  yet  the  combination  of  this  turning  with  the  revolu- 
tion on  the  long  axis  permits  the  animal  to  reach  any  conceivable  position 
with  relation  to  the  environment.  In  other  words,  Paramecium,  in  spite 
of  its  curious  limitations  as  to  method  of  movement,  is  as  free  to  vary  its 
relations  to  the  environment  in  response  to  a  stimulus  as  an  organism 
of  its  form  and  structure  could  conceivably  be.  Such  behavior  does  not 
fall  within  the  concept  of  a  reflex,  if  the  latter  is  defined  as  a  uniform 
reaction. 

Still  less  does  the  behavior  of  Stentor  yield  itself  to  formulation  as 
purely  reflex.  To  the  same  stimulus,  under  the  same  external  conditions, 
this  animal  may  react,  as  we  have  seen,  in  several  different  ways;  its 
reaction  depends  upon  its  physiological  condition.  The  same  is  true 
for  Hydra  and  other  Ccelenterata,  for  the  echinoderm,  the  flatworm,  and 
many  other  invertebrates,  as  we  have  set  forth  in  detail  in  the  descrip- 
tion of  the  behavior  of  these  organisms.  In  the  sea  anemone  we  have 
examples  of  indecision,  parts  of  the  positive  reaction  being  combined 
with  parts  of  the  negative.  In  all  these  cases  the  behavior  is  far  from 
that  sureness  and  fixity  that  characterizes  the  supposed  reflex. 

Even  in  Amoeba  it  is  difficult  to  apply  the  reflex  concept  to  the  be- 
havior. So  far  are  the  reactions  here  from  being  uniform,  that  we  can 
almost  say,  on  the  contrary,  that  Amoeba  never  does  the  same  thing 
twice.  The  behavior  is  here  formless,  undefined,  not  held  within  nar- 
row bounds  by  structural  conditions,  as  in  the  infusoria  and  in  most 
higher  animals;  the  essential  criteria  of  reflex  action  seem  lacking.  It 
would  be  very  difficult  to  apply  the  reflex  concept,  for  example,  to  the 


280  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

behavior  of  a  floating  Amoeba  in  attaining  a  solid  support,  as  described 
on  page  8,  or  to  the  food  reaction  illustrated  in  Fig.  21.  Further,  as 
we  have  seen  on  page  20,  Amceba  may  at  different  times  react  in  oppo- 
site ways  to  the  same  stimulus. 

Indeed,  consideration  shows  that  it  is  impossible  to  apply  rigidly  the 
conception  of  a  reflex,  as  an  invariable  reaction  to  a  definite  stimulus, 
to  the  behavior  of  any  organism  having  more  than  one  motor  reaction 
at  its  command.  James  ("Psychology,"  Vol.  I,  p.  21)  and  Pearl  (1903, 
p.  704)  have  given  us  sketches  of  what  would  be  the  behavior  of  an 
organism  whose  acts  were  purely  reflex.  Taking  the  reaction  to  food 
as  an  example,  James  says :  "The  animal  will  be  condemned  fatally  and 
irresistibly  to  snap  at  it  whenever  presented,  no  matter  what  the  cir- 
cumstances may  be;  he  can  no  more  disobey  this  prompting  than  water 
can  refuse  to  boil  when  a  fire  is  kindled  under  the  pot.  His  life  will 
again  and  again  pay  the  forfeit  of  his  gluttony.  Exposure  to  retaliation, 
to  other  enemies,  to  traps,  to  poisons,  to  the  dangers  of  repletion,  must 
be  regular  parts  of  his  existence.  His  lack  of  all  thought  by  which  to 
weigh  the  danger  against  the  attractiveness  of  the  bait,  and  of  all  voli- 
tion to  remain  hungry  a  little  while  longer,  is  the  direct  measure  of  his 
lowness  in  the  mental  scale"  (I.e.,  p.  21).  Such  a  picture  has  only  to 
be  presented  to  make  us  see  the  impossibility  of  constructing  the  entire 
behavior  of  an  organism  out  of  such  irresistible  reflexes.  For  the  re- 
actions to  dangers  and  enemies  must  then  be  reflexes,  as  well  as  the 
reactions  to  food,  and  the  two  are  incompatible.  Suppose  the  food  and 
the  danger  are  present  together,  as  often  happens.  The  organism  can- 
not react  fatally  and  irresistibly  to  both,  for  the  movements  required  are 
in  opposite  directions.  It  must  decide  to  react  either  with  relation  to 
one  or  to  neither,  and  in  either  case  the  fatality  and  irresistibility  of  at 
least  one  of  the  reflexes  disappears. 

If,  then,  we  consider  the  reflex  an  invariable  reaction  to  a  given  stimu- 
lus, we  cannot  hold  that  behavior  in  lower  organisms  is  made  up  of 
reflexes.  Indeed,  the  fact  that  stands  out  most  clearly  in  the  behavior 
is  the  following:  Each  stimulus  causes  as  a  rule  not  merely  a  single 
definite  action  that  may  be  called  a  reflex,  but  a  series  of  "trial"  move- 
ments, of  the  most  diverse  character,  and  including  at  times  practically 
all  the  movements  of  which  the  animal  is  capable.  The  reaction  to  a 
given  stimulus  depends  on  the  physiological  state  of  the  organism,  not 
alone  on  its  anatomical  structure ;  and  physiological  states  are  variable. 
This  is  true  both  for  the  infusoria  and  for  man. 

The  attempt  to  characterize  the  behavior  of  the  lower  organisms  as 
purely  reflex  has  risen  from  the  desire  to  show  that  the  structural  con- 
ditions of  the  organism  and  the  physical  and  chemical  action  of  the 


REFLEXES  IN  BEHAVIOR  281 

stimulus  are  sufficient  to  account  for  their  behavior,  without  the  neces- 
sary intervention  of  consciousness.  This  is  well  expressed  by  v.  Uexkiill 
(1897,  p.  306)  when  he  says  that  we  are  to  regard  the  reflex  as  "the 
necessary  course  of  a  process  that  is  conditioned  by  nothing  else  than 
the  mechanical  structure  of  the  organism."  Shall  we  include  the  phys- 
iological state  of  the  organism  as  part  of  its  mechanical  structure?  If 
we  answer  this  question  in  the  negative,  then  it  is  clear  that  the  behavior 
of  the  lower  organisms  is  not  reflex  in  character.  If  on  the  other  hand 
we  answer  this  question  in  the  affirmative,  holding  that  the  physiological 
state  is  some  chemical  or  physical  configuration  of  the  substance  of  the 
organism,  and  therefore  to  be  included  in  its  mechanical  structure,  then 
the  entire  question  concerning  the  reflex  character  of  behavior  in  a  given 
organism  loses  its  objective  character  and  evaporates  into  thin  air.  For 
in  the  highest  as  well  as  the  lowest  organism  the  reactions  must  be  sup- 
posed to  depend  upon  the  physical  and  chemical  constitution  of  the 
organism,  unless  we  are  to  accept  vitalism.  And  if  when  we  say  that 
the  behavior  of  an  organism  is  reflex  in  character,  we  mean  only  that 
its  behavior  depends  upon  its  physical  and  chemical  make-up,  we  can 
make  no  distinction  upon  this  ground  between  the  behavior  of  lower 
and  higher  organisms.  This  point  is  indeed  well  recognized  by  thought- 
ful psychologists.  "The  conception  of  all  action  as  conforming  to  this 
[the  reflex]  type  is  the  fundamental  conception  of  modern  nerve  physi- 
ology," says  James  ("Principles  of  Psychology,"  Vol.  I,  p.  23).  Those 
who  have  been  most  strenuous  in  attempting  to  demonstrate  that  the 
behavior  of  certain  lower  organisms  is  "purely  reflex"  in  character  would 
probably  be  the  last  to  hold  that  in  the  higher  organisms  behavior  must 
be  explained  on  essentially  different  principles.  The  attempt  often 
made  to  contrast  the  behavior  of  lower  organisms  as  reflex  with  that 
of  higher  organisms  as  something  else,  seems  therefore  a  shortsighted 
and  pointless  proceeding.  What  a  given  organism  does  under  stimu- 
lation is  limited  by  its  action  system,  and  within  these  limits  is  deter- 
mined largely  by  its  physiological  condition  at  the  time  stimulation 
occurs.  In  the  lowest  organism  the  action  system  confines  the  varia- 
tions in  behavior  within  rather  narrow  limits,  and  the  different  physio- 
logical conditions  distinguishable  are  few  in  number ;  hence  the  behavior, 
is  less  varied  than  in  higher  animals.  But  the  difference  is  one  of  degree, 
not  of  kind.  The  behavior  of  Paramecium  and  the  sea  urchin  is  reflex 
if  the  behavior  of  the  dog  and  of  man  is  reflex ;  objective  evidence  does 
not  indicate  that  there  is  from  this  point  of  view  any  fundamental  differ- 
ence in  the  cases. 

The  importance  attributed  to  the  concept  of  reflex  action  is  of  course 
due  to  the  desire  to  find  a  simple  invariable  unit  for  behavior,  compa- 


282  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

rable  to  the  atom  in  physics.  To  obtain  such  a  unit  it  is  necessary  to  take 
into  consideration  as  an  additional  possible  variable,  the  physiological 
state  of  the  organism.  Dr.  E.  G.  Spaulding  has  suggested  the  follow- 
ing: We  cannot  properly  say  for  a  given  organism  "same  stimulus, 
same  reaction,"  as  appears  to  be  the  usual  idea  of  a  reflex.  On  the 
other  hand  we  can  say  "same  physiological  state,  same  stimulus,  same 
reaction,"  and  this  supplies  whatever  need  there  may  be  for  a  simple 
invariable  element  of  behavior.  To  this  element  the  term  "reflex"  or 
an  equivalent  one  might  be  applied,  and  we  might  then  maintain  that 
the  behavior  of  all  organisms  is  made  up  of  reflexes.  But  on  this  defi- 
nition the  question  whether  the  behavior  of  a  given  organism  is  made 
up  of  reflexes  is  not  a  problem  for  objective  investigation;  but  the  con- 
ception that  it  is  thus  made  up  is  a  postulate,  in  accordance  with 
which  we  interpret  the  results  of  our  observations ;  and  this  applies  to 
the  highest  as  well  as  to  the  lowest  organisms.  The  assumption  that 
varied  physiological  states  exist  is  of  course  one  of  these  interpretations, 
made  to  save  what  is  essentially  this  very  postulate,  —  the  principle 
that  like  causes  always  produce  like  effects. 

LITERATURE   XV 
Reflexes  and  Behavior 

Hobhouse,  1 901 ;  James,  190 1 ;  Beer,  Bethe,  and  v.  Uexkull,  1899;  Titch- 
ener,  1902;  Driesch,  1903;   v.  Uexkull,  1897. 


CHAPTER   XVI 

ANALYSIS   OF   BEHAVIOR   IN  LOWER   ORGANISMS 

i.    The  Causes  and  Determining  Factors  of  Movements  and 

Reactions 

In  the  following  sections  we  shall  analyze  the  behavior  of  the  lower 
organisms  described  in  previous  chapters,  attempting  to  determine  the 
essential  characteristics  of  behavior  and  to  bring  out  the  chief  factors 
of  which  it  is  made  up.  We  shall  take  up  first  the  factors  causing  or 
determining  the  movements  and  reactions,  treating  first  the  inner,  then 
the  outer,  factors.  Then  we  shall  consider  the  movements  and  reactions 
themselves,  attempting  to  bring  out  the  features  of  essential  importance. 
From  a  synthesis  of  our  results  on  both  sets  of  factors  —  the  causes  and 
the  effects  —  we  shall  try  to  arrive  at  a  general  statement  of  the  funda- 
mental character  of  behavior  in  the  lower  organisms. 

The  external  factors  in  behavior  are  usually  known  as  stimuli,  and 
their  effects  on  movement  as  reactions.  The  term  "  reaction  "  has  been 
used  in  various  ways.  In  our  analysis  we  shall  employ  the  word  "reac- 
tion" as  signifying  an  actual  change  in  movement.  The  word  is  some- 
times used  in  a  looser  sense.  For  example,  the  movement  toward  a 
source  of  light  is  often  spoken  of  as  the  reaction  to  light,  even  though  the 
only  observable  change  of  movement  was  that  by  which  orientation  was 
brought  about.  This  looser  sense  is  sometimes  unavoidable,  either  from 
our  ignorance  of  the  facts,  or  for  other  reasons ;  when  used  in  this  loose 
sense  in  the  following,  the  context  will  clearly  indicate  it.  Where  ques- 
tion might  arise,  reacton  is  to  be  understood  as  meaning  an  observable 
change  of  movement.  To  avoid  ambiguity,  the  latter  phrase  will  some- 
times be  used  in  place  of  the  word  "  reaction."  The  following  discussion 
will  be  intelligible  only  if  this  meaning  of  the  word  "reaction"  is  kept  in 
mind. 

A.    The  Internal  Factors 

(i)  Activity  does  not  require  Present  External  Stimulation.  — A  first 
and  essential  point  for  the  understanding  of  behavior  is  that  activity 
occurs  in  organisms  without  present  specific  external  stimulation.     The 

283 


284  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

normal  condition  of  Paramecium  is  an  active  one,  with  its  cilia  in  rapid 
motion ;  it  is  only  under  special  conditions  that  it  can  be  brought  partly 
to  rest.  Vorticella,  as  Hodge  and  Aikins  (1895)  showed,  is  at  all  times 
active,  never  resting.  The  same  is  true  of  most  other  infusoria  and,  in 
perhaps  a  less  marked  degree,  of  many  other  organisms.  Even  if  external 
movements  are  suspended  at  times,  internal  activities  continue.  The 
organism  is  activity,  and  its  activities  may  be  spontaneous,  so  far  as 
present  external  stimuli  are  concerned. 

The  spontaneous  activity,  of  course,  depends  finally  on  external 
conditions,  in  the  same  sense  that  the  existence  of  the  organism  depends 
on  external  conditions.  The  movements  are  undoubtedly  the  expression 
of  energy  derived  from  metabolism.  The  organism  continually  takes 
in  energy  with  its  food  and  in  other  ways,  and  continually  gives  off 
this  energy  in  activities  of  various  sorts.  The  point  of  importance  is 
that  this  activity  often  depends  more  largely  on  the  past  external 
conditions  through  which  the  energy  was  stored  up  than  upon  present 
ones.  Thus  the  organism  may  move  without  the  present  action  of 
anything  that  may  be  pointed  out  as  a  specific  external  stimulus  to 
this  movement. 

This  fact  is  of  great  importance  for  understanding  behavior,  and 
many  errors  have  arisen  from  its  neglect.  If  we  see  an  organism  moving, 
it  is  not  necessary  to  assume  that  some  external  stimulus  now  acting  is 
producing  this  movement.  In  studying  the  reactions  to  present  particu- 
lar stimuli,  as  light  or  gravity  or  a  chemical,  it  is  in  many  cases  not 
necessary  to  account  for  the  fact  of  movement,  for  the  movement  comes 
from  the  discharge  of  internal  energy,  and  often  the  organism  was  moving 
(though  perhaps  in  another  direction)  before  the  stimulus  began  to  act. 
It  is  only  the  change  in  the  movement  when  the  stimulus  acts  that  the 
present  stimulus  must  account  for.  In  the  movement  of  Paramecium 
toward  the  cathode,  it  is  not  necessary  to  assume,  as  some  have  done, 
that  a  special  force  (as  cataphoric  action)  is  required,  to  carry  the  ani- 
mals. They  were  moving  equally  before  the  electric  current  began  to 
act;  the  difference  that  the  stimulus  has  made  is  in  the  direction  of 
motion,  and  it  is  only  this  that  the  stimulus  must  account  for.  In  the 
movements  of  infusoria  toward  chemicals,  some  have  supposed  that  an 
attractive  force  from  the  chemical  was  necessary,  actually  bearing  the 
organisms  along;  this  is  quite  superfluous.  In  general,  when  an 
organism  moves  toward  or  away  from  any  agent,  it  is  unnecessary  to 
assume  that  an  actually  attractive  or  repellent  transporting  force  is  act- 
ing upon  it.  Often  —  perhaps  usually  in  the  lower  organisms  —  move- 
ment in  a  certain  direction  is  due  only  to  the  release  of  inhibition.  The 
organism  moves  in  the  given  direction  because  it  is  moving  from  internal 


ANALYSIS   OF  BEHAVIOR   IN   LOWER   ORGANISMS         285 

impulse,  and  because  movement  in  this  direction  is  not  prevented. 
This  possibility  must  be  considered  in  all  cases. 

Further,  when  the  action  of  a  stimulus  actually  changes  the  direction 
of  movement  in  an  organism,  persistence  in  this  new  direction  by  no 
means  demands  persistence  in  stimulation.  The  new  direction  once 
attained  may  be  followed,  from  the  internal  impulse  to  movement, 
merely  because  there  is  nothing  to  change  this  direction,  or  because 
stimulation  does  occur  when  this  direction  is  changed,  bringing  the 
organism  back  to  it.  This  is  apparently  the  case,  as  we  have  seen,  in 
the  reactions  of  infusoria  to  gravity,  to  water  currents,  and  to  light  com- 
ing from  a  certain  direction. 

Often,  of  course,  stimulation  does  rouse  an  organism  to  increased 
activity.  But  even  in  this  case  the  activity  is  due  to  the  release  of  in- 
ternal energy.  It  may,  therefore,  continue  long  after  the  stimulation 
which  inaugurated  the  release  has  ceased  to  act.  Such  continuance 
thus  does  not  necessarily  imply  continued  action  of  the  stimulus.  In 
many  cases  the  specific  stimulus  to  action  is  only  the  change  of  conditions. 
Thus,  if  light  or  a  chemical  acts  upon  an  organism,  the  only  stimulus 
may  be  the  sudden  change,  even  though  the  organism  continues  to 
move  after  the  conditions  have  become  constant.  Whether  the  effective 
stimulation  actually  continues,  must  be  determined  by  experiment;  it 
cannot  be  simply  assumed. 

In  general,  when  an  organism  is  moving  in  a  certain  way  —  even 
when  toward  or  from  a  certain  agent  —  careful  analytical  experimenta- 
tion is  necessary  to  determine  whether  this  movement  is  due  to  present 
stimulation,  or  to  the  simple  outflow  of  the  stored-up  energy  of  the  or- 
ganism through  the  channels  provided  by  its  structure.  In  most  cases, 
apparently,  the  latter  is  true. 

The  spontaneous  activities  of  the  organism  —  those  not  due  directly 
to  present  specific  external  stimulation  —  are,  perhaps,  the  most  im- 
portant factors  in  its  behavior. 

(2)  Activity  may  change  without  External  Cause.  —  If  we  watch  a 
specimen  of  Vorticella  under  uniform  conditions,  we  find  that  its  behavior 
does  not  remain  uniform.  At  first  the  animal  is  outstretched,  its  cilia 
bringing  a  current  of  water  to  the  mouth.  After  a  certain  period  its 
stalk  contracts,  its  peristome  folds  inward,  and  its  cilia  cease  moving. 
Soon  it  extends  and  resumes  its  normal  activity.  These  alternations  of 
different  ways  of  behaving  occur  at  rather  regular  intervals,  though  the  ex- 
ternal conditions  remain  unchanged.  Hydra  shows  parallel  changes  of 
behavior  at  intervals,  under  uniform  external  conditions  (p.  189) ;  the 
medusa  contracts  at  intervals,  though  there  is  no  change  in  the  outer  con- 
ditions, and  similar  examples  could  be  given  for  many  other  organisms. 


286  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

(3)  Changes  in  Activity  depend  on  Changes  in  Physiological  States.  — 
What  causes  the  changes  in  behavior  described  in  the  foregoing  para- 
graph ?  Since  the  external  conditions  have  not  changed,  the  animal 
itself  must  have  changed.  The  Vorticella  which  contracts  and  folds  its 
cilia  is  in  certain  respects  a  different  animal  from  the  one  that  remains 
extended  and  keeps  its  cilia  in  active  motion,  otherwise  it  would  not  act 
thus  differently.  Its  internal  or  physiological  condition  has  been  changed. 
Soon  its  original  condition  is  restored ;  it  unfolds  and  behaves  as  it  did 
at  first.  In  the  same  way,  the  physiological  condition  of  the  Hydra 
that  stands  quiet  with  outspread  arms  is  different  from  that  of  the  Hydra 
which,  without  external  cause,  contracts  and  changes  its  position.  The 
behavior  produced  by  these  differences  in  physiological  condition  is  the 
same  as  that  producible  by  an  external  stimulus. 

Other  examples  of  changes  in  behavior  due  to  changed  physiologi- 
cal states  are  shown  in  the  different  reactions  of  hungry  and  of 
well-fed  individuals,  which  we  have  seen  in  so  many  cases,  and  in  the 
different  reactions  of  organisms  as  determined  by  their  respiratory 
processes. 

The  precise  nature  of  these  internal  changes  of  condition  we  of 
course  do  not  know.  The  expression  "physiological  states"  evidently 
includes  a  great  many  things  of  heterogeneous  character,  having  merely 
the  common  characteristic  that  they  are  internal  modifications  of  the 
living  substance  resulting  in  changed  behavior.  In  the  lower  organisms 
it  is  difficult  to  define  the  different  classes  of  physiological  states  in  an 
objective  way,  though  the  progress  of  investigation  will  doubtless  make 
this  possible.  Certain  fundamental  differences  in  diverse  states  will  be 
pointed  out  in  the  following  pages. 

(4)  Reactions  to  External  Agents  depend  on  Physiological  States.  — 
Change  of  activity  is,  of  course,  often  produced  by  external  agents. 
With  this  point  we  are  to  deal  later ;  here  what  interests  us  is  the  fact 
that  in  any  given  organism  the  reaction  to  a  given  external  agent  de- 
pends on  the  physiological  condition  of  the  organism.  This  principle 
is  of  such  importance  that  we  must  dwell  upon  it. 

First  we  have  the  important  fact  that  the  reaction  to  a  given  stimulus 
depends  upon  the  progress  of  the  metabolic  processes.  To  a  given 
external  condition  the  nature  of  the  reaction  often  depends  upon  whether 
it  favors  these  metabolic  processes.  If  material  for  these  processes  is 
lacking,  the  reaction  to  stimuli  is  of  such  a  character  as  to  secure  such 
material.  In  such  organisms  as  the  ccelenterates  almost  the  whole 
character  of  the  behavior,  down  to  the  details  of  the  reactions  to  specific 
stimuli,  depends  thus  on  the  condition  of  the  processes  of  metabolism 
(sec  Chapter  XI).     The  behavior  of  organisms  is  similarly  determined 


ANALYSIS   OF  BEHAVIOR    IN   LOWER   ORGANISMS        287 

by  the  course  of  other  internal  processes ;   these  are,  perhaps,  the  most 
important  factors  determining  physiological  states. 

Of  a  somewhat  different  character  are  the  changes  in  physiological 
state  exemplified  in  the  behavior  of  Stentor  and  the  flatworm.  In  Sten- 
tor,  as  we  have  seen  in  Chapter  X,  we  can  distinguish  at  least  five  differ- 
ent physiological  states  in  which  the  same  individual  reacts  differently 
to  the  same  conditions.  Under  stimulation  by  numerous  grains  of  car- 
mine in  the  water,  the  Stentor  in  condition  No.  1  does  not  react  at  all. 
In  condition  No.  2  it  reacts  by  turning  into  a  new  position.  In  condition 
No.  3  its  reaction  is  a  reversal  of  the  ciliary  current.  In  No.  4  it  responds 
by  contracting  at  brief  intervals.  In  No.  5  the  contractions  are  stronger 
and  the  organism  remains  longer  in  the  contracted  condition,  finally 
breaking  its  attachment  to  its  tube  and  swimming  away.  Throughout 
this  entire  series  of  reactions  the  external  conditions  remain  the  same, 
so  that  we  can  attribute  the  different  reactions  only  to  different  condi- 
tions of  the  organism. 

In  the  flatworm  we  have  seen  in  Chapter  XII  that  six  different  physio- 
logical conditions  may  be  distinguished,  in  each  of  which  the  flatworm 
is  a  different  animal,  so  far  as  its  reactions  to  stimuli  are  concerned. 
We  need  not  repeat  the  details  regarding  these  conditions  here.  Illus- 
trations of  the  fact  that  the  reaction  of  the  organism  depends  on  its 
physiological  state  might  be  drawn  from  the  behavior  of  many  other 
animals. 

(5)  .The  Physiological  State  may  be  changed  by  Progressive  Internal 
Processes,  particularly  those  of  metabolism.  The  well-fed  sea  anemone 
or  Hydra  is  a  very  different  animal,  so  far  as  its  behavior  is  concerned, 
from  the  specimen  that  has  fasted.  Under  uniform  conditions,  the  sea 
anemone  that  is  well  fed  remains  quiet;  while  the  individual  that  has 
exhausted  the  material  for  metabolism  toils  painfully  away  on  a  tour  of 
exploration.  The  well-fed  individual  reacts  negatively  or  not  at  all 
to  that  to  which  the  hungry  individual  reacts  positively.  The  Para- 
mecium bursar  id  that  has  exhausted  its  supply  of  oxygen  behaves  in  one 
way  with  regard  to  light,  the  individual  in  which  respiration  is  progress- 
ing normally  in  another  way.  Innumerable  examples  illustrating  this 
principle  can  be  found  in  the  behavior  of  lower  and  higher  organisms. 
It  is  hardly  too  much  to  say  that  the  progress  of  the  metabolic  and  other 
physiological  processes  is  the  chief  factor  in  determining  the  behavior 
of  lower  organisms. 

(6)  The  Physiological  State  may  be  changed  by  the  Action  0}  External 
Agents. — This  follows  directly  from  the  behavior  of  Stentor  and  the 
flatworm,  to  which  we  have  referred  in  the  preceding  paragraph.  The 
Stentor  in  condition  No.  1,  as  we  have  seen,  does  not  respond  to  the 


/ 


288  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

stimulus  of  the  carmine  grains  in  the  water.  The  stimulus  continues, 
and  after  a  time  the  physiological  condition  changes  so  that  the  animal 
does  respond.  The  change  in  physiological  state  can  then  be  due  only 
to  the  action  of  the  stimulus.  In  the  same  way  the  other  changes  in  the 
physiological  condition  of  Stentor  and  the  flatworm  are  evidently  due 
largely,  at  least,  to  the  continued  action  of  the  stimulus. 

(7)  The  Physiological  Slate  may  be  changed  by  the  Activity  of  the 
Organism.  —  This  is  demonstrated  by  the  spontaneous  changes  in  the 
behavior  of  Vorticella  or  Hydra,  of  which  we  have  already  spoken.  At 
first  the  animal  is  in  a  certain  condition  which  corresponds  to  extension 
and  activity.  It  then  passes  into  a  condition  which  results  in  contrac- 
tion. But  it  does  not  remain  contracted ;  the  contraction  itself  restores 
the  original  condition,  so  that  the  animal  now  again  extends  and  becomes 
active.  Certain  of  the  changes  in  physiological  state  seen  in  Stentor 
and  the  flatworm  are  probably  clue  to  the  reactions  of  the  organism. 
Thus,  we  find  that  the  flatworm,  after  turning  for  a  long  time  away  from 
a  lateral  stimulus,  suddenly  changes  and  turns  in  the  opposite  direction 
(p.  253).  The  change  of  physiological  state  conditioning  this  change  of 
reaction  was  probably  due,  not  alone  to  the  continuance  of  the  stimu- 
lus, but  to  the  previous  prolonged  turning  of  the  flatworm  in  a  certain 
direction. 

(8)  External  Agents  cause  Reaction  by  changing  the  Physiological 
State  0}  the  Organism.  —  We  have  found  that  external  stimuli  cause 
changes  in  physiological  state,  and  that  changes  in  physiological  state 
induce  changes  in  behavior,  —  activities  of  a  definite  character.  It  is 
evident,  then,  that  external  agents  must  change  the  behavior  of  organisms 
by  changing  their  physiological  condition.  In  other  words,  in  a  reaction 
to  an  external  stimulus  the  course  of  events  is  probably  as  follows : 
The  stimulus  causes  first  a  change  in  the  physiological  condition  of  the 
organ  or  organism.  This,  then,  causes  a  change  in  behavior,  which 
we  call  a  reaction  to  the  stimulus.  What  the  organism  reacts  to  is 
the  change  produced  within  it  by  the  external  agent.  Hence,  if  two 
different  external  agents  induce  the  same  internal  change  (as  by  block- 
ing certain  processes)  they  will  receive  the  same  reaction. 

(9)  The  Behavior  0}  the  Organism  at  any  Moment  depends  upon  its 
Physiological  State  at  that  Moment.  —  This  follows  immediately  from 
the  principles  already  developed.  We  have  seen  that  both  in  "spon- 
taneous" movements  and  in  reactions  to  stimuli  the  behavior  depends 
on  the  physiological  condition  of  the  animal.  The  behavior  must  then 
depend,  secondarily,  not  only  upon  the  present  external  stimulus,  but 
upon  all  the  conditions  which  affect  the  physiological  states.  This 
point  will  be  developed  under  the  two  succeeding  heads. 


ANALYSIS  OF  BEHAVIOR  IN  LOWER  ORGANISMS        289 

(10)  Physiological  Slates  change  in  Accordance  with  Certain  Laws.  — 
It  is  evident  that  we  may  distinguish  at  least  two  great  classes  of  physio- 
logical states,  —  those  depending  on  the  progress  of  the  metabolic 
processes  of  the  organism,  and  those  otherwise  determined.  The  changes 
in  the  metabolic  states,  as  we  may  call  the  former,  of  course  depend  largely 
upon  the  laws  of  metabolism.  In  the  physiological  states  not  directly 
dependent  on  metabolism,  but  rather  upon  stimulation  and  upon  the 
activity  of  the  organism,  such  as  we  have  seen  in  Stentor,  we  find  certain 
fairly  well-defined  laws  of  change,  of  a  peculiar  character. 

In  a  number  of  organisms  we  have  found  the  following  phenomenon : 
Under  certain  conditions  the  organism  reacts  in  a  certain  way.  These 
conditions  continuing,  the  organism  changes  its  first  reaction  for  a  second 
or  third  or  fourth.  Later  the  same  external  conditions  recur,  and  now 
the  organism  at  once  responds,  not  by  its  first  reaction,  but  by  its  final 
one.  This  is  illustrated  for  unicellular  organisms  by  the  case  of  Stentor 
(Chapter  X);  for  higher  Metazoa  it  is  well  seen  in  the  behavior  of  cer- 
tain Crustacea,  as  described  by  Yerkes  and  Spaulding  (Chapter  XII). 
There  are  certain  differences  in  these  two  cases  that  will  be  taken  up 
later. 

How  does  this  state  of  affairs  come  about?  The  "physiological 
state  "  is  evidently  to  be  looked  upon  as  a  dynamic  condition,  not  as 
a  static  one.  It  is  a  certain  way  in  which  bodily  processes  are  taking 
place,  and  tends  directly  to  the  production  of  some  change.  In  this 
respect  the  "law  of  dynamogenesis,"  propounded  for  ideas  of  movement 
in  man,  applies  to  it  directly  (see  Baldwin,  1897,  p.  167);  ideas  must 
indeed  be  considered,  so  far  as  their  objective  accompaniments  are  con- 
cerned, as  certain  physiological  states  in  higher  organisms.  The  changes 
toward  which  the  physiological  state  tends  are  of  two  kinds.  First  the 
physiological  state  (like  the  idea)  tends  to  produce  movement.  This 
movement  often  results  in  such  a  change  of  conditions  as  destroys  the 
physiological  state  under  consideration.  But  in  case  it  does  not,  then 
the  second  tendency  of  the  physiological  state  shows  itself.  It  tends  to 
resolve  itself  into  another  and  different  state.  Condition  1  passes  to 
condition  2,  and  this  again  to  condition  3.  This  tendency  shows  itself 
even  when  the  externaL  conditions  remain  uniform. 

In  this  second  tendency  a  most  important  law  manifests  itself.  When 
a  certain  physiological  state  has  been  resolved,  through  the  continued 
action  of  an  external  agent  or  otherwise,  into  a  second  physiological 
state,  this  resolution  becomes  easier,  so  that  in  the  course  of  time  it 
takes  place  quickly  and  spontaneously. 

This  may  be  illustrated  from  the  behavior  of  Stentor,  as  described 
in  Chapter  X  as  follows :  When  the  organism  is  stimulated  by  the  flood 


290  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

of  carmine  grains  (or  in  any  other  way),  this  produces  immediately  a 
certain  physiological  state  (corresponding  to  that  accompanying  a  sensa- 
tion in  ourselves) ;  this  state  we  may  call  A.  This  state  at  first  produces 
no  reaction.  As  the  carmine  continues  or  is  repeated,  this  state  A  passes 
to  a  second  state  B,  producing  a  bending  to  one  side.  (The  two  may 
differ  only  slightly,  but  a  difference  must  exist,  otherwise  B  would  not 
produce  a  reaction  while  A  does  not.)  After  several  repetitions  of  the 
stimulus,  the  condition  B  passes  to  the  condition  C,  producing  a  reversal 
of  the  cilia,  and  this  finally  passes  to  D,  resulting  in  a  contraction  of  the 
body.  The  course  of  the  changes  in  physiological  states  may  then  be 
represented  as  follows :  — 

A — ^B — ^C — ^D 


Now  we  find  that  after  many  repetitions  of  the  stimulation  the  or- 
ganism contracts  at  once  as  soon  as  the  carmine  comes  in  contact  with 
it.  In  other  words,  the  first  condition  A  passes  at  once  to  the  condition 
D,  and  this  results  in  immediate  contraction. 

A-+D 


It  seems  probable  that  the  same  series  occurs  as  before,  save  that  con- 
ditions B  and  C  are  now  passed  rapidly  and  in  a  modified  way,  so  that 
they  do  not  result  in  a  reaction,  but  are  resolved  directly  into  D.  The 
process  would  then  be  represented  as  follows :  — 

A — ^B' — ^C — ^D 

But  whatever  the  intermediate  conditions,  it  is  clear  that  after  the 
state  A  has  become  resolved,  through  pressure  of  external  conditions, 
into  state  D,  this  resolution  takes  place  more  readily,  occurring  at  once 
after  the  state  A  is  reached. 

The  same  law  is  illustrated  in  the  experiments  of  Yerkes  and  Spauld- 
ing  on  much  higher  organisms.  In  the  experiments  of  Spaulding 
with  the  hermit  crabs  (Chapter  XII),  the  introduction  of  the  screen  and 
the  diffusion  of  the  juices  of  the  fish  cause  the  animals  to  move  about. 
In  so  doing  they  reach  the  dark  screen,  which  induces,  let  us  say,  the 
physiological  condition  A.  This  leads  to  no  special  reaction.  But 
this  is  followed  regularly  by  contact  with  food,  inducing  the  physiological 
condition  B,  which  is  concomitant  with  a  positive  reaction.  The  physio- 
logical condition  A  is  thus  regularly  resolved  into  the  condition  B. 
In  the  course  of  time  this  resolution  becomes  automatic,  so  that  as  soon 
as  the  condition  A  is  reached  it  passes  at  once  to  B.  The  positive  reac- 
tion concomitant  with  B  is  therefore  given  even  though  the  original  cause 
of  B  is  absent. 


ANALYSIS  OF  BEHAVIOR  IN  LOWER   ORGANISMS         291 

In  the  experiments  of  Yerkes,  using  the  two  passages  to  the  water, 
described  in  Chapter  XII,  the  following  are  the  conditions.  The  pres- 
ence of  the  investigator  or  the  drying  of  the  animal  at  T,  Fig.  139,  acts 
as  a  stimulus  to  cause  movement  away  from  T.  A  turn  to  the  right  is 
accompanied,  let  us  say,  by  the  physiological  condition  A.  This  is 
soon  followed  by  contact  with  the  glass  plate  G,  inducing  the  condition 
B,  which  involves  inhibition  of  movement  and  a  turn  in  another  direction. 
In  the  course  of  time  the  condition  A  comes  to  be  resolved  immediately 
into  B,  so  that  movement  is  inhibited  at  the  start.  On  the  other  hand,  the 
physiological  condition  C,  concomitant  with  a  turn  to  the  left,  is  regularly 
resolved  into  the  condition  D,  concomitant  with  reaching  the  water,  and 
inducing  a  positive  reaction.  This  resolution  becomes  automatic,  so 
that  the  turn  to  the  left  is  followed  at  once  by  forward  motion  to 
the  water.  In  these  cases  the  actual  number  of  physiological  states 
that  could  be  distinguished  is,  of  course,  greater  than  what  we  have 
set  forth  above.  But  this  does  not  alter  in  any  way  the  general 
principle  involved. 

The  law  of  the  resolution  of  physiological  states  illustrated  in  the 
foregoing  examples  is  of  the  highest  importance  for  the  understanding 
of  behavior.  With  selection  from  among  varied  movements,  it  forms 
one  of  the  corner-stones  for  the  development  of  behavior.  The  law 
may  be  expressed  briefly  as  follows :  — 

The  resolution  oj  one  physiological  state  into  another  becomes  easier 
and  more  rapid  after  it  has  taken  place  a  number  0}  times.  Hence  the 
behavior  primarily  characteristic  for  the  second  state  comes  to  follow 
immediately  upon  the  first  state. 

The  operations  of  this  law  are,  of  course,  seen  on  a  vast  scale  in  higher 
organisms,  in  the  phenomena  which  we  commonly  call  memory,  asso- 
ciation, habit  formation,  and  learning.  In  the  lower  organisms  the  mani- 
festations of  this  law  are  comparatively  little  known.  This  is  probably 
due  largely  to  difficulties  of  experimentation.  Since  the  law  has  been 
demonstrated  to  hold  in  unicellular  organisms  (Stentor  and  Vorticella), 
there  is  much  reason  to  suppose  that  it  is  general,  and  that  it  will  be 
demonstrated  in  one  form  or  another  for  other  lower  organisms.  There 
seems  to  be  no  theoretical  reason  for  supposing  it  to  be  limited  to  higher 
animals.  Very  great  differences  exist  among  different  organisms  as  to 
the  ease  with  which  the  quick  resolution  of  one  physiological  state  into 
another  is  established.  There  are  likewise  great  differences  in  the  per- 
manency of  existing  connections  among  the  present  reaction  methods. 
Hence  it  does  not  follow,  as  Yerkes  (1902)  has  well  pointed  out,  that  be- 
cause a  few  experiments  do  not  demonstrate  this  law  in  a  given  case, 
the  law,  therefore,  does  not  hold.     In  his  experiments  with  crustaceans, 


292  BEHAVIOR   OF   THE  LOWER  ORGANISMS 

Yerkes  found  that  a  very  large  number  of  repetitions  were  necessary 
before  a  given  resolution  was  established. 

(n)  Different  Factors  on  which  Behavior  Depends.  — We  have  seen 
that  the  behavior  of  the  organism  at  a  given  moment  depends  on  its 
physiological  state,  and  that  it  therefore  secondarily  depends  upon  all 
the  factors  upon  which  the  physiological  state  depends.  Hence  we  can- 
not expect  the  behavior  to  be  determined  alone  by  the  present  external 
stimulus,  as  is  sometimes  maintained,  for  this  is  only  one  factor  in 
determining  the  physiological  state.  The  behavior  at  a  given  moment 
may  depend  on  the  following  factors,  since  these  all  affect  the  physio- 
logical state  of  the  organism :  — 

i.   The  present  external  stimulus. 

2.  Former  stimuli. 

3.  Former  reactions  of  the  organism. 

4.  Progressive  internal  changes  (due  to  metabolic  processes,  etc.). 

5.  The  laws  of  the  resolution  of  physiological  states  one  into  another. 
All  these  factors  have  been  strictly  demonstrated  by  observation  and 

experiment,  even  in  unicellular  organisms.  Any  one  of  these  alone, 
or  any  combination  of  these,  may  determine  the  activity  at  a  given 
moment. 


CHAPTER  XVII 

ANALYSIS   OF   BEHAVIOR    {Continued) 

B.     The  External  Factors  in  Behavior 

(i)  As  we  have  seen  in  the  foregoing  chapter,  external  agents  produce 
reactions  through  the  intermediation  of  changes  in  the  internal  physio- 
logical condition  of  the  organism.  This  proposition  is,  perhaps,  a  truism, 
yet  it  needs  to  be  kept  in  mind  if  behavior  is  to  be  understood.  In  the 
following  discussion  it  will  be  unnecessary  to  mention  specifically  in  each 
case  the  intermediate  step  in  the  process. 

(2)  The  most  general  external  cause  of  a  reaction  is  a  change  in  the 
conditions  affecting  the  organism.  This  has  been  illustrated  in  detail 
in  the  descriptive  portions  of  the  present  work.  In  most  cases  the  change 
which  induces  a  reaction  is  brought  about  by  the  organism's  own  move- 
ments. These  cause  a  change  in  the  relation  of  the  organism  to  the 
environment;  to  these  changes  the  organism  reacts.  The  whole  be- 
havior of  free-moving  organisms  is  based  on  the  principle  that  it  is  the 
movements  of  the  organism  that  have  brought  about  stimulation;  the 
regulatory  character  of  the  reactions  induced  is  intelligible  only  on  this 
basis.  Reactions  due  to  stimulation  produced  in  this  manner  are  seen 
when  an  organism  progresses  from  a  cooler  to  a  warmer  region,  or  vice 
verscL;  when  it  moves  into  or  out  of  a  chemical  in  solution;  when  it 
strikes  in  its  course  against  a  hard  object ;  when  the  unoriented  infuso- 
rian  shows  lateral  movements  while  subjected  to  light  coming  from  one 
side.  In  all  these  cases  it  is  the  movement  of  the  organism  which  causes 
a  change  in  its  relation  to  the  external  agent,  and  this  change  produces 
reaction.  In  most,  if  not  all,  cases  the  change  is  one  in  the  intensity  of 
some  agent  acting  on  the  organism. 

But  an  active  change  in  the  environmental  conditions,  not  produced 
by  movement  of  the  organism,  may  likewise  produce  reaction ;  this  is, 
of  course,  most  frequently  the  case  in  fixed  organisms,  such  as  the  sea 
anemone.  Responses  produced  in  this  way  are  seen  in  the  reactions  of 
organisms  when  heated  or  cooled  from  outside,  or  when  a  chemical 
or  a  solid  object  is  brought  in  contact  with  them,  or  when  the  source 
of  light  changes  in  intensity  or  position,  or  when  the  direction  of  a  water 

293 


294  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

current  changes.     The  general  fact  is  that  a  change  in  the  environment 
produces  a  change  in  behavior. 

A.  Change  of  conditions  often  produces  a  change  of  movement  when 
neither  the  preceding  nor  the  following  condition  would,  acting  continu- 
ously, produce  any  such  effect.  Thus  when  Euglena  is  swimming 
toward  the  source  of  light,  if  the  light  is  suddenly  diminished,  the  organism 
reacts  by  a  change  in  its  course ;  it  then  returns  to  its  course  and  continues 
to  swim  toward  the  light  as  before.  Its  behavior  before  and  after  the 
change  is  the  same;  but  at  the  moment  of  change  there  is  a  reaction. 
Paramecium  may  live  and  behave  normally  in  water  at  20  degrees  or  at 
30  degrees,  yet  a  change  from  one  to  the  other,  or  a  much  less  marked 
change,  produces  a  definite  reaction.  This  relation  could  be  illustrated 
by  many  cases  from  the  behavior  of  any  of  the  organisms  described  in  the 
foregoing  pages.     Thus  change  simply  as  change  may  produce  reaction. 

To  constant  conditions,  on  the  other  hand,  unless  differing  very 
greatly  from  the  normal,  the  organism  usually  does  not  react.  The 
Paramecium  placed  in  A^  per  cent  sodium  chloride  reacts  at  first,  but 
soon  resumes  its  normal  behavior.  Euglena  or  Stentor  when  subjected 
to  changes  in  the  illumination  of  the  anterior  end  react  till  they  come 
into  a  position  of  orientation  where  these  changes  cease ;  they  then  swim 
forward  in  the  normal  manner.  As  a  general  rule,  organisms  soon  be- 
come acclimatized  to  a  continuous  condition,  if  it  is  not  too  intense. 
Exceptions  to  this  rule  will  be  considered  later. 

Of  course  a  change  must  reach  a  certain  amount  before  reaction  is 
produced;  that  is,  there  is  a  certain  necessary  threshold  of  stimulation. 
In  the  best-known  cases  the  amount  of  the  change  which  produces  re- 
action is  proportional  to  the  intensity  of  the  original  condition ;  in  other 
words,  the  relation  of  stimulus  to  reaction  follows  Weber's  law  (see  pp. 
38,  123).  That  is,  it  is  relative  change,  not  absolute  change,  that  causes 
reaction. 

B.  But  not  every  change,  even  if  sufficiently  marked,  produces 
reaction.  It  is  usually  not  change  alone  that  determines  reaction,  but 
change  in  a  certain  direction.  Of  two  opposite  changes,  one  usually 
produces  a  certain  reaction,  while  the  other  either  produces  none  or 
brings  about  a  reaction  of  opposite  character.  This  point  is  one  that 
is  of  fundamental  importance  for  an  understanding  of  behavior.  It 
may  be  illustrated  in  its  simplest  aspect  from  the  behavior  of  the  infusoria, 
where  any  reaction  that  is  produced  is  usually  of  such  a  character  as  to 
remove  the  organism  from  the  source  of  stimulation  (the  "avoiding 
reaction").  Paramecium  at  a  temperature  of  28  degrees  reacts  thus 
negatively  to  a  change  to  a  higher  temperature,  not  to  the  opposite  change. 
Paramecium  at  22  degrees  reacts  to  a  decrease  of  temperature,  not  to 


ANALYSIS  OF  BEHAVIOR  IN  LOWER   ORGANISMS         295 

an  increase.  Stentor  reacts  to  an  increase  of  illumination,  not  to  a 
decrease.  Euglena  when  moderately  lighted  reacts  negatively  to  a 
decrease  of  illumination,  not  to  an  increase ;  if  strongly  lighted,  it  shows 
the  opposite  relations.  Paramecium  reacts  at  passing  into  an  alkaline 
solution,  but  not  at  passing  out ;  it  reacts  at  passing  out  of  a  weak  acid 
solution,  not  at  passing  in.  Hydra  at  24  degrees  reacts  to  an  increase 
of  2  degrees  in  temperature,  not  to  an  equivalent  decrease.  Innumerable 
instances  of  this  fact  could  be  given  from  the  behavior  of  the  lower 
organisms. 

What  decides  whether  a  given  change  or  its  opposite  shall  produce 
this  negative  reaction?  Examination  of  the  facts  brings  out  the  follow- 
ing relations :  The  organism  generally  reacts  by  a  change  in  its  behavior 
when  the  change  is  of  such  a  nature  as  to  lead  away  from  the  optimum. 
By  optimum  we  mean  here  the  conditions  most  favorable  to  the  life 
processes  of  the  organism  in  question.  Changes  leading  toward  this 
optimum  produce  in  many  animals  no  reaction;  the  organisms  simply 
continue  the  activity  which  has  brought  about  this  change.  Changes 
leading  away  from  the  optimum  produce  a  negative  reaction,  by  which 
the  organism  is  removed  from  the  operation  of  this  change.  There  are 
undoubtedly  some  limitations  and  exceptions  to  this,  and  with  these  we 
shall  have  to  deal  later,  but,  as  we  have  seen  for  Paramecium,  it  is  un- 
questionably the  rule.  Cases  where  this  rule  does  not  hold  are  striking 
because  exceptional.  Reaction  in  this  manner  keeps  the  infusoria  in 
regions  of  moderate  temperature,  prevents  them  from  entering  injurious 
chemical  substances,  brings  green  organisms  such  as  Euglena  into  the 
light,  where  their  metabolic  activities  are  aided,  and  in  general  keeps 
the  organisms  in  regions  where  the  conditions  are  favorable.  In  these 
organisms  the  chief  cause  of  reaction  to  a  change  is  its  interference  with 
the  normal  life  activities,  and  the  reaction  if  successful  serves  to  remove 
the  interference. 

C.  But  in  many  cases  changes  which  favor  the  normal  activities 
produce  reaction.  The  response  is  then  of  such  a  character  as  to  retain 
the  organism  under  the  conditions  producing  the  change.  Such  re- 
sponses we  usually  call  positive  reactions.  In  many  cases  it  is  clear  that 
such  reactions  are  determined  by  a  previously  existing  unfavorable 
state  of  metabolism  or  of  other  processes.  The  Hydra  or  the  sea 
anemone  does  not  react  positively  to  food  substances  unless  metabolism 
is  in  such  a  state  as  to  require  more  material;  and  parallel  relations 
exist  in  the  behavior  of  many  if  not  all  organisms.  In  unicellular  or- 
ganisms definite  positive  reactions  play  a  comparatively  small  part, 
favorable  conditions  being  secured  primarily  by  a  negative  reaction  to 
less  favorable  conditions.     It  is  possible  that  all  positive  reactions  are 


296  BEHAVIOR   OF    THE  LOWER   ORGANISMS 

to  be  traced  to  this  as  the  primitive  type  (see  the  following  chapter). 
That  is,  while  the  negative  reaction  is  impelled  by  new  unfavorable  con- 
ditions, tending  to  retain  the  more  favorable  old  condition,  the  positive 
reaction  is  impelled  by  the  old  unfavorable  condition,  tending  to  retain 
the  new  more  favorable  one. 

(3)  Sometimes  change  of  behavior  occurs  without  change  in  the 
environment,  the  external  conditions  remaining  uniform.  As  a  rule, 
we  have  found  that  change  of  behavior  occurs  under  uniform  conditions 
only  when  these  are  decidedly  injurious  to  the  organism.  If  the  water 
containing  infusoria  or  the  flat  worm  is  heated  to  about  37  degrees,  the 
animals  react  not  merely  to  the  change  in  temperature;  they  continue 
to  react  violently,  with  frequent  alternations  in  the  behavior,  until  they 
die.  Many  examples  could  be  given  of  such  reactions.  Under  uniform 
conditions  a  change  in  behavior  also  occurs  at  times  owing  to  internal 
changes.  The  commonest  cases  of  this  sort  are  the  changes  in  behavior 
due  to  hunger.  In  almost  all  cases  of  reaction  under  uniform  conditions 
we  find  that  the  reaction  is  due  to  some  interference  with  the  normal 
life  processes.  But  reactions  under  uniform  conditions  play  only  a 
small  part  in  the  behavior,  as  compared  with  reactions  to  changes. 

We  have  then  two  main  results  as  regards  the  external  causes  of 
changes  in  behavior:  (1)  change  alone  may  produce  reaction;  (2)  inter- 
ference with  the  normal  life  processes  or  release  from  such  interference 
may  produce  reaction.  The  usual  cause  of  a  change  in  behavior  is  a 
combination  of  both  these  factors  —  a  change  that  hinders  or  helps  the 
normal  life  processes.  In  the  lowest  organisms  it  is  chiefly  interfering 
changes  that  cause  reaction. 

(4)  Reactions  to  Representative  Stimuli.  —  In  the  reactions  due  to 
change,  one  further  point  is  of  much  importance.  The  organism  may 
react  to  changes  that  in  themselves  neither  favor  nor  interfere  with  the 
normal  life  activities,  but  which  do  lead  to  such  favor  or  interference. 
The  reaction  given  is  then  positive  or  negative  in  correspondence  with 
the  benefit  or  injury  to  which  the  change  leads.  Thus,  Stentor  may 
bend  toward  a  small  solid  body  when  touched  by  it  (Fig.  83),  this  reac- 
tion aiding  it  to  procure  food,  though  there  is  no  indication  that  the 
touch  itself  is  directly  beneficial.  Or  it  may  contract  away  from  a 
light  touch,  this  enabling  it  to  escape  from  a  possible  approaching  enemy, 
though  the  touch  itself  is  not  injurious.  Euglena  reacts  negatively 
when  its  colorless  anterior  end  alone  is  shaded,  yet  it  is  only  when  the 
shadow  affects  its  chlorophyll  bodies  that  it  interferes  with  metabolism. 
The  flatworm  may  turn  toward  a  weak  stimulus  of  any  sort.  This 
leads  in  the  long  run  to  its  obtaining  food,  though  sometimes  the 
stimulus  does  not  come  from  a  food  body.     In  such  cases  the  animal 


ANALYSIS   OF  BEHAVIOR  IN   LOWER  ORGANISMS         297 

reacts  positively  merely  to  the  localized  change,  not  to  the  nature  of 
the  change.  Certain  colorless  infusoria,  and  the  white  Hydra,  react 
to  light  in  such  a  way  as  to  gather  at  the  lightest  side  of  the  vessel 
containing  them.  There  is  no  evidence  that  the  light  itself  is  beneficial 
to  them,  but  their  reaction  does  aid  them  in  obtaining  food,  since  their 
prey  gathers  on  the  lightest  side  of  the  vessel.  The  collecting  of  Para- 
mecia  in  C02  can  hardly  be  considered  to  favor  directly  the  life  processes 
of  the  animals,  but  it  apparently  aids  them  to  obtain  food.  The  sea 
urchin  tends  to  remain  in  dark  places,  and  light  is  apparently  injurious 
to  it.  Yet  it  responds  to  a  sudden  shadow  falling  upon  it  by  pointing 
its  spines  in  the  direction  from  which  the  shadow  comes.  This  action 
is  defensive,  serving  to  protect  it  from  enemies  that  in  approaching  may 
have  cast  the  shadow.  The  reaction  is  produced  by  the  shadow,  but  it 
refers,  in  its  biological  value,  to  something  behind  the  shadow. 

In  all  these  cases  the  reaction  to  the  change  cannot  be  considered 
due  to  any  direct  injurious  or  beneficial  effect  of  the  actual  change  itself. 
The  actual  change  merely  represents  a  possible  change  behind  it,  which 
is  injurious  or  beneficial.  The  organism  reacts  as  if  to  something  else 
than  the  change  actually  occurring;  the  change  has  the  function  of  a 
sign.  We  may  appropriately  call  stimuli  of  this  sort  representative 
stimuli. 

This  reaction  to  representative  stimuli  is  evidently  of  the  greatest  value, 
from  the  biological  standpoint.  It  enables  organisms  to  flee  from  injury 
even  before  the  injury  occurs,  or  to  go  toward  a  beneficial  agent  that  is 
at  a  distance.  Such  reactions  reach  an  immense  development  in  higher 
animals ;  most  of  our  own  reactions,  for  example,  are  to  such  representa- 
tive stimuli.  Only  as  we  react  to  actual  physical  pain  or  pleasure  do  we 
share  with  lower  organisms  the  fundamental  reaction  to  direct  injury  or 
benefit.  Practically  all  our  reactions  to  things  seen  or  heard  are  such 
reactions  to  representative  stimuli.  While  such  behavior  plays  a  much 
larger  part  in  higher  than  in  lower  organisms,  the  existence  of  reactions 
to  representative  stimuli  even  in  the  low  organisms  considered  in  the 
present  work  is  an  evident  fact. 

How  can  we  account  for  such  reactions  ?  It  is  perhaps  worth  while 
to  point  out  that  the  operation  of  the  law  of  the  resolution  of  physiologi- 
cal states,  set  forth  on  page  291,  would  result  naturally  in  the  production 
of  such  reactions.  Let  us  take  as  the  simplest  possible  case  the  reaction 
of  Euglena  when  its  colorless  anterior  tip  is  shaded.  Since  it  is  only 
the  metabolism  of  the  chlorophyll  bodies  that  is  blocked  by  shade,  we 
cannot  suppose  that  the  shading  of  the  colorless  tip  actually  interferes 
with  the  life  processes.  Yet  to  this  change  Euglena  reacts  negatively. 
We  may  suppose  that  the  shading  of  this  colorless  part  induces  the  indif- 


298  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

ferent  physiological  state  A,  which  of  itself  produces  no  reaction.  But 
this  is  invariably  followed  by  the  shading  of  the  chlorophyll  bodies, 
interfering  with  metabolism  and  inducing  the  physiological  state  B,  re- 
sulting in  a  negative  reaction.  Thus  the  state  A  is  regularly  resolved 
into  the  state  B.  In  accordance  with  the  law  of  the  resolution  of  physio- 
logical states,  this  resolution  in  the  course  of  time  becomes  spontaneous. 
A  passes  at  once  to  B  and  a  negative  reaction  occurs,  even  when  the 
colorless  anterior  tip  alone  is  shaded.  In  unicellular  organisms  a  condi- 
tion so  reached  would  naturally  continue  to  succeeding  generations,  since 
the  organisms  in  reproducing  merely  divide. 

In  the  same  way  the  defensive  reaction  of  the  sea  urchin  when 
shaded  could  be  produced.  The  condition  A,  induced  by  the  shade,  is 
usually  resolved  into  the  condition  B,  induced  by  the  attack  of  an  enemy, 
and  resulting  in  the  defensive  movement.  This  resolution  in  the  course 
of  time  may  then  become  spontaneous,  so  that  the  sea  urchin  now  reacts 
defensively  even  when  a  cloud  passes  over  the  sun.  This  condition 
could  be  continued  to  succeeding  generations  only  if  acquired  charac- 
ters are  inherited. 

Thus  through  the  operation  of  the  law  of  the  resolution  of  physio- 
logical states  the  following  general  result  will  be  produced :  If  a  given 
agent  induces  a  physiological  state  A,  and  this  is  usually  followed  by  a 
second  state  B,  then  in  time  the  given  agent  will  produce  at  once  the 
response  due  primarily  to  B.  The  organism  will  have  come  to  react 
to  A  as  representative  of  B. 

We  do  not  know  whether  the  development  of  reactions  to  representa- 
tive stimuli  has  actually  taken  place  in  this  way,  or  not.  But  the  fact 
that  there  is  a  factor,  whose  existence  is  demonstrated,  that  would  pro- 
duce exactly  these  results,  certainly  suggests  strongly  the  probability 
that  they  have  been  at  least  partly  brought  about  in  the  way  above  set 
forth.  If  the  law  of  the  resolution  of  physiological  states  is  actually 
operative  throughout  behavior,  the  effect  would  be  to  make  behavior 
depend  on  the  results  of  the  animal's  own  action.  This  would  produce 
behavior  that  is  regulatory,  such  as  we  actually  find  to  exist. 

(5)  The  reaction  to  a  given  external  stimulus  depends,  as  we  have 
previously  seen,  on  the  physiological  condition  of  the  organism,  not 
alone  on  the  nature  of  the  external  change.  The  physiological  condi- 
tion depends  partly  on  whether  the  normal  stream  of  life  activities  is 
proceeding  uninterruptedly.  In  certain  physiological  states,  such  as 
hunger,  the  processes  are  not  proceeding  normally.  This  impels  the 
organism  to  a  change,  so  that  to  almost  any  external  stimulus  it  may 
react  in  a  way  that  tends  to  bring  about  a  change.  The  hungry  sea 
anemone  in  this  condition  reacts  positively  to  all  sorts  of  neutral  bodies; 


ANALYSIS   OF  BEHAVIOR  IN  LOWER   ORGANISMS         299 

the  hungry  Hydra  reacts  positively  to  chemicals.  In  certain  physio- 
logical conditions  the  flatworm  reacts  positively  to  almost  any  stimulus. 
At  other  times  the  opposite  conditions  prevail;  the  animal  reacts  nega- 
tively to  the  stimulus  to  which  it  before  reacted  positively.  In  closely 
related  organisms  differing  in  their  metabolic  processes,  the  reaction  to 
a  given  agent  depends  on  the  nature  of  the  metabolic  processes,  tending 
to  retain  the  conditions  favoring  these  processes.  This  is  especially 
well  illustrated  in  the  bacteria  (pp.  36,  39)  and  in  the  ccelenterates 
(pp.  224,  231),  but  is  equally  true  for  other  organisms.  Thus  what  the 
organism  does  depends  on  the  course  of  its  life  processes,  and  upon  the 
completeness  or  incompleteness  of  their  performance.  In  other  words, 
the  behavior  of  the  animal  under  stimulation  corresponds  to  its  needs, 
and  is  determined  by  them.  This  correspondence  is  of  course  not  al- 
ways perfect ;  with  this  point  we  can  deal  after  we  have  considered  the 
nature  of  the  reactions  given.  But  a  study  of  the  determining  factors 
of  behavior  demonstrates  that  the  relation  of  external  conditions  to  in- 
ternal processes  is  the  chief  factor,  and  that  hence  behavior  is  regulatory 
in  essential  nature. 

(6)  We  may  sum  up  the  external  factors  that  produce  or  determine 
reactions  as  follows:  (1)  The  organism  may  react  to  a  change,  even 
though  neither  beneficial  nor  injurious.  (2)  Anything  that  tends  to 
interfere  with  the  normal  current  of  life  activities  produces  reactions  of 
a  certain  sort  ("negative").  (3)  Any  change  that  tends  to  restore  or 
favor  the  normal  life  processes  may  produce  reactions  of  a  different  sort 
("positive").  (4)  Changes  that  in  themselves  neither  interfere  with 
nor  assist  the  normal  stream  of  life  processes  may  produce  negative  or 
positive  reactions,  according  as  they  are  usually  followed  by  changes 
that  are  injurious  or  beneficial.  (5)  Whether  a  given  change  shall  pro- 
duce reaction  or  not,  often  depends  on  the  completeness  or  incomplete- 
ness of  the  performance  of  the  metabolic  processes  of  the  organism 
under  the  existing  conditions.  This  makes  the  behavior  fundament- 
ally regulatory. 


CHAPTER  XVIII 

ANALYSIS   OF  BEHAVIOR    (Continued) 

2.     The  Nature  of  the  Movements  and  Reactions 

In  the  preceding  section  we  have  dealt  primarily  with  the  causes  and 
conditions  of  movements  and  reactions ;  here  we  are  to  deal  with  the 
movements  and  reactions  themselves. 

A.     The  Action  System 

Every  organism  has  certain  characteristic  ways  of  acting,  which  are 
conditioned  largely  by  its  bodily  structure,  and  which  limit  its  action 
under  all  sorts  of  conditions.  This  perhaps  seems  a  mere  truism. 
Amoeba  of  course  cannot  swim  through  the  water  like  Paramecium,  and 
the  latter  cannot  fly  through  the  air  nor  walk  about  on  dry  land.  But 
the  behavior  of  any  given  lower  organism  is  actually  confined  in  this  way 
within  narrower  limits  than  is  frequently  recognized.  Formulae  have 
at  times  been  proposed  to  explain  the  movements  of  various  organisms, 
when  the  latter  are  incapable  of  performing  the  movements  called  for 
by  the  formulae.  It  is  usually  possible  to  determine  with  some  approach 
to  completeness  the  various  movements  which  a  given  organism  has  at 
command.  These  form  as  a  rule  a  coordinated  system,  which  we  have 
called  in  previous  pages  the  action  system.  The  action  system  of  an 
organism  determines  to  a  considerable  extent  the  way  it  shall  behave 
under  given  external  conditions.  Under  the  same  conditions,  organisms 
of  different  action  systems  must  behave  differently,  for  to  any  stimulus 
the  response  must  be  by  some  component  of  the  action  system.  Thus, 
Amoeba,  the  bacteria,  Paramecium,  Hydra,  and  the  flatworm  have  ac- 
tion systems  of  different  character,  and  their  behavior  under  given  con- 
ditions must  differ  accordingly.  This  matter  has  been  dealt  with  in 
detail  in  the  descriptive  portion  of  the  present  work,  so  that  we  need  not 
dwell  upon  it  here.  In  studying  the  behavior  of  any  organism,  the  first 
requisite  to  an  understanding  is  the  working  out  of  the  action  system.1 

1  The  action  system  corresponds  largely  to  what  Putter  (1904)  calls  the  "  Symptoma- 
tology" of  organisms. 


ANALYSIS  OF  BEHAVIOR  IN  LOWER   ORGANISMS         301 
B.    Negative  Reactions 


-,v 


In  our  discussion  of  the  causes  of  reaction  we  found  that  we  could 
classify  most  stimuli  into  two  groups  —  those  that  interfere  with  the  nor- 
mal life  processes,  and  those  that  do  not.  It  will  be  best  to  consider 
separately  the  reactions  to  these  two  classes  of  stimulation,  and  to  take 
up  the  reactions  to  unfavorable  stimuli  first,  since  these  seem  to  present 
the  most  primitive  conditions. 

The  simplest  reaction  to  unfavorable  stimuli  is  merely  a  change  in 
the  direction  or  character  of  the  movement.  The  organism  is  moving 
in  a  certain  direction;  when  subjected  to  an  unfavorable  change,  it 
changes  its  direction  of  movement.  This  is  the  case  in  Amoeba,  in  bac- 
teria, in  infusoria,  in  rotifera,  in  the  flatworm;  indeed,  in  most  free 
organisms.  The  mere  fact  of  a  change  is  in  itself  regulatory  or  adap- 
tive. The  original  behavior  has  brought  on  the  unfavorable  change, 
hence  the  best  thing  to  do  is  to  change  this  behavior.  If  the  unfavor- 
able condition  still  persists,  the  behavior  is  changed  again ;  this  being 
continued,  the  organism  is  bound  to  escape  from  the  unfavorable  condi- 
tions if  it  is  possible  to  do  so.  The  repeated  change  in  behavior  under 
unfavorable  stimulation  is  very  striking  in  Paramecium,  in  Stentor,  in 
Hydra,  in  the  flatworm,  and  elsewhere. 

The  fundamental  principle  for  this  method  of  reaction  is  that  a 
change  0}  behavior  under  unfavorable  conditions  is  in  itself  regulatory. 
As  we  have  before  pointed  out,  the  reactions  of  organisms  are  based  on 
the  principle,  usually  correct,  that  it  is  the  previous  behavior  of  the 
organism  that  has  brought  on  the  present  conditions.  Hence  if  these 
conditions  are  unfavorable,  a  change  of  behavior  is  required. 

The  developments  of  this  method  of  behavior  found  indifferent  organ- 
isms consist  in  defining,  varying,  and  systematizing  the  changes  that 
occur.  In  Amoeba  we  find  perhaps  the  simplest  condition.  When  this 
animal  in  its  forward  course  meets  unfavorable  conditions  it  merely  goes 
in  some  other  direction.  In  what  direction  it  will  go  cannot  be  predicted 
from  either  the  structure  of  the  organism  or  from  the  localization  of 
the  stimulus,  for  Amoeba  can  move  with  any  part  in  advance.  It  is  evi- 
dently determined  by  transient  internal  conditions.  In  organisms  with 
definite  body  axes  and  other  structural  relations,  the  change  of  motion 
becomes  more  definite.  In  bacteria  the  organism  moves  after  stimula- 
tion in  the  opposite  direction.  In  the  free-swimming  infusoria,  as  illus- 
trated by  Paramecium,  and  in  the  free  Rotifera,  there  is  an  elaborate 
system  of  movements  which  make  the  reaction  effective.  The  animal 
stops  or  reverses  the  movement  which  has  -brought  on  the  unfavorable 
condition,  then  swings  its  anterior  end  about  in  a  circle  as  it  moves  for- 


302  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

ward,  so  as  to  try  successively  many  different  directions.  The  behavior 
shows  the  "method  of  trial"  reduced  to  a  system.  It  would  be  almost 
impossible  to  suggest  any  modification  of  this  reaction,  as  exemplified 
in  Paramecium,  that  would  make  it  better  fitted,  under  the  given  rela- 
tions, for  meeting  all  sorts  of  conditions.  In  fixed  infusoria,  such  as 
Stentor,  this  behavior  is  modified  to  adapt  it  to  the  fixed  life.  In  the 
free-swimming  animal  the  organism  is  subjected  to  new  conditions  every 
time  the  reaction  is  repeated,  hence  there  is  little  occasion  to  try  other 
methods  of  behavior.  But  if  the  organism  is  fixed  in  one  place,  this  is 
not  true ;  when  a  given  reaction  is  repeated  it  merely  brings  on  the  same 
conditions  its  first  performance  induced.  So  different  methods  are  de- 
veloped. Under  unfavorable  conditions  the  organism  first  turns  to  one 
side,  then  reverses  its  ciliary  current,  then  contracts,  etc.  (see  p.  174), 
trying  many  different  changes  of  behavior.  In  Hydra,  in  the  starfish, 
in  the  flatworm,  we  have  seen  this  same  "method  of  trial"  appearing 
under  various  forms.  In  all  these  organisms  persistent  unfavorable 
stimulation  induces  first  one  physiological  state,  then  another,  then 
another,  and  to  each  state  there  corresponds  a  certain  method  of 
behavior. 

C.     Selection  from  the  Conditions  produced  by  Varied  Movements 

In  all  this  behavior  we  find  the  manifestations  of  a  most  important 
principle,  one  of  far-reaching  significance  for  the  understanding  of  be- 
havior. The  stimulus  does  not  produce  directly  a  single  simple  move- 
ment (a  reflex  act),  of  a  character  that  relieves  the  organism  at  once 
from  the  stimulating  condition.  On  the  contrary,  stimulation  is  followed 
by  many  and  varied  movements,  from  which  the  successful  motion  is 
selected  by  the  fact  that  it  is  successful  in  causing  cessation  of  stimula- 
tion. This  is  the  principle  of  the  "selection  of  overproduced  move- 
ments," of  which  much  use  has  justly  been  made  by  Spencer,  Bain,  and 
especially  by  Baldwin  (1897,  1902),  in  attempting  to  explain  behavior. 
It  is  more  accurate  to  speak  of  the  selection  of  the  proper  conditions  of  the 
environment  through  varied  movements.  It  is  primarily  the  proper  en- 
vironmental conditions  that  are  selected;  the  movements  are  only  a 
means  to  that  end.  From  this  point  of  view  what  we  have  often  called 
in  the  foregoing  pages  the  method  of  trial  may  be  formulated  as  follows : 
When  stimulated  the  organism  performs  movements  which  subject  it  to 
varied  conditions.  When  in  this  way  it  reaches  a  condition  that  relieves 
it  of  stimulation  the  reacton  movement  ceases,  since  there  is  no  further 
cause  for  it.  The  organism  may  then  resume  its  usual  movements.  In 
the  case  where  the  reaction  consists  of  changes  in  direction,  as  in  infuso- 


ANALYSIS  OF  BEHAVIOR   IN  LOWER  ORGANISMS         303 

ria,  the  resumption  of  the  usual  forward  motion  of  course  carries  the 
organism  in  a  new  direction  brought  about  by  the  reaction. 

What  movements  are  produced  by  the  stimulating  agent  depends 
on  the  action  system  of  the  organism;  it  performs  the  movements  that 
it  is  accustomed  to  perform.  In  some  cases  these  movements  are  of  a 
rather  uniform  character,  yet  are  of  such  a  nature  as  to  subject  the  ani- 
mal to  many  changes  of  the  environmental  conditions.  This  is  the  case, 
for  example  in  the  reactions  of  such  infusoria  as  Paramecium.  In 
other  cases  the  movements  themselves  are  varied;  the  organism  first 
reacts  in  one  way,  then  in  another,  running  thus  through  a  whole  series 
of  activities,  till  one  succeeds  in  ridding  the  organism  of  the  stimulating 
condition.  This  is  the  method  of  behavior  seen  in  Stentor  and  in  most 
higher  organisms.  In  both  methods  the  essential  point  is  the  same 
—  the  subjection  of  the  organism  to  varied  environmental  conditions, 
until  one  of  these  relieves  it  from  the  stimulation.  This  condition  is 
then  said  to  be  "selected."  In  some  cases  the  maintenance  of  this 
favorable  environmental  condition  involves  continuance  of  the  move- 
ment finally  resulting  from  the  varied  trial  movements ;  in  other  cases 
it  does  not. 

Reaction  by  selection  of  excess  movements  depends  largely  on  the 
fact,  previously  brought  out  (p.  283),  that  the  movement  itself  is  not 
directly  produced  by  the  stimulus.  The  movement  is  due,  as  we  have 
seen,  to  the  internal  energy  of  the  organism.  In  the  case  of  free-moving 
animals  like  Paramecium,  stimulation  usually  neither  increases  nor  de- 
creases the  amount  of  motion,  but  merely  causes  it  to  change  in  various 
ways.  Reaction,  of  course,  sometimes  does  take  the  form  of  an  increase 
of  motion ;  this  is  seen  in  the  increased  movements  of  infusoria  under 
strong  chemicals  or  heat ;  of  Planaria  under  light,  etc.  But  even  in 
these  cases  the  energy  for  the  motion  comes  from  within  and  is  merely 
released  by  the  action  of  the  stimulus.  It  is  important  to  remember,  if 
the  behavior  is  to  be  understood,  that  energy,  and  often  impulse  to  move- 
ment, come  from  within,  and  that  when  they  are  released  by  the  stimu- 
lus, this  is  merely  what  James  has  called  "trigger  action."  There  is 
thus  no  reason  to  expect  that  upon  stimulation  an  organism  will  perform 
merely  a  single  simple  movement  (a  "reflex  action"),  and  then  become 
quiet.  Movement  of  one  sort  or  another  is  its  natural  condition,  and 
after  stimulation  has  ceased  it  may  show  movements  (the  character  or 
direction  of  which  may  have  been  determined  by  the  stimulus)  for  an. 
indefinite  period. 

Behavior  by  selection  from  the  results  of  varied  movements  is  based 
on  general  principles.  The  reactions  are  not  specific  ones,  definitely 
adapted  to  particular  kinds  of  stimulation,  but  are  responses  to  any 


3°4 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


stimulation  of  a  certain  general  character,  —  namely,  to  any  condition 
that  interferes  with  the  normal  course  of  the  life  processes.  On  re- 
ceiving an  unfavorable  stimulus  that  it  has  never  before  experienced, 
the  organism  behaving  on  this  plan  is  not  at  a  loss  for  some  method 
of  reacting;  it  merely  responds  in  the  usual  way,  performing  one  move- 
ment after  another,  till  one  of  these  relieves  it  of  the  stimulation,  if  this 
is  possible. 

Of  course  special  circumstances  may  arise  in  which  this  general 
method  of  reacting  may  be  ineffective.  If  dropped  into  a  strong  chemi- 
cal, Paramecium  reacts  in  the  usual  manner,  though  this  does  not  help 
it.  If  the  water  containing  a  flatworm  is  heated,  the  animal  goes 
through,  one  after  the  other,  almost  every  reaction  it  has  at  command, 
though  all  are  unavailing  (p.  245).  The  difficulty,  of  course,  lies  in  the 
fact  that  under  these  circumstances  nothing  the  organism  can  do  is  of 
any  avail,  and  a  man  in  similar  conditions  would  be  equally  helpless. 
The  infusorian  and  the  flatworm,  like  the  man,  merely  try  everything 
possible  before  succumbing. 

D.    "Discrimination" 
The  effectiveness  of  reaction   bv  continued  varied   movements  in 

J 

preserving  the  organism  depends  upon  several  factors.  One  of  these  is 
what  is  called  in  higher  animals  the  power  of  discrimination,  —  that  is, 
the  accuracy  with  which  the  tendency  to  react  is  adjusted  to  the  injuri- 
ousness  of  the  stimulating  agent.  If  an  injurious  agent  resembles  in 
its  first  action  a  non-injurious  one,  so  that  the  animal  reacts  in  the  same 
way  toward  both,  its  behavior  will  not  preserve  it  from  injury.  Using 
the  more  subjective  form  of  expression,  if  the  organism  does  not  discrimi- 
nate between  the  first  action  of  injurious  and  non-injurious  agents,  it 
cannot  react  differently  to  them,  until  perhaps  the  injury  has  become 
irremediable.  The  facts  show  that  in  both  higher  and  lower  organisms 
the  power  of  discrimination  under  weak  stimulation  is  far  from  perfect. 
Thus,  in  the  sense  in  which  we  have  used  the  term,  Paramecium  dis- 
criminates acids  from  alkalies  and  salts,  and  these  again  from  sugar. 
But  it  does  not  effectively  discriminate  the  first  effects  of  different  acid 
substances,  so  that  it  swims  into  weak  carbonic  acid,  which  is  harmless, 
and  likewise  into  weak  sulphuric  acid  and  copper  sulphate,  which  kill  it. 
It  does  not  discriminate  the  first  action  of  a  10  per  cent  sugar  solution 
from  that  of  water,  hence  it  swims  readily  into  the  sugar  solution  and  is 
killed  by  the  osmotic  action.  In  all  these  cases  it  does  discriminate  and 
react  to  the  injurious  agent  when  its  effect  has  become  marked,  but 
injury  has  then  already  occurred  and  the  reaction  does  not  preserve  the 


ANALYSIS   OF   BEHAVIOR   IN   LOWER  ORGANISMS         305 

animal.  In  regard  to  these  injurious  substances  Paramecium  thus 
makes  what  we  would  call  in  ourselves  a  "mistake."  The  whole 
scheme  of  reaction  by  the  selection  of  the  results  of  varied  movements 
is  not  a  set,  perfected,  final  one,  but  is  a  tentative  plan,  based  on  the  con- 
fusing world  taken  as  it  comes ;  it  is  liable  to  mistakes,  and  is  capable  of 
development.  Progress  in  this  method  of  behavior  takes  place  largely 
through  increase  in  the  accuracy  of  discrimination  of  different  stimuli. 
This  may  occur  through  the  law  of  the  increased  readiness  of  resolution 
of  physiological  states  after  repetition,  in  the  way  that  we  shall  attempt 
to  set  forth  later  (Chapter  XIX). 

E.   Adaptivcness  of  Movements 

The  second  chief  factor  on  which  depends  the  effectiveness  of 
behavior  by  selection  of  overproduced  movements  lies  in  the  relative 
fitness  of  the  movements  to  relieve  the  organism  from  the  unfavorable 
conditions.  This,  of  course,  depends  on  many  things.  If  a  powerful 
chemical  is  diffusing  from  a  certain  direction,  the  rapid  movements  of 
Paramecium  are  more  likely  to  save  than  is  the  slow  motion  of  Amoeba. 
There  are  two  factors  on  which  the  effectiveness  of  the  movements 
depends,  that  are  worthy  of  special  consideration. 

In  what  we  may  call  the  pure  method  of  trial,  a  most  important  re- 
quirement for  effectiveness  is  that  the  movements  shall  be  so  varied  as 
to  give  much  opportunity  for  finding  other  conditions.  There  are  great 
differences  in  the  behavior  of  different  organisms  from  this  standpoint. 
This  may  be  illustrated  by  a  comparison  of  the  reactions  of  Paramecium 
and  Bursaria  to  heat,  as  previously  described.  When  a  portion  of  the 
area  containing  the  organisms  is  heated,  these  two  infusoria  react  in 
accordance  with  essentially  the  same  plan,  yet  practically  none  of  the 
Paramecia  are  injured,  while  a  large  proportion  of  the  Bursariae  are 
killed.  The  difference  is  due  chiefly  to  the  fact  that  Paramecium 
rapidly  repeats  its  reactions  and  revolves  on  its  long  axis  as  it  turns,  so 
that  in  a  short  time  it  has  tried  in  a  really  systematic  way  many  different 
directions,  and  is  practically  certain  to  find  one  leading  away  from  the 
heated  region,  if  such  exists.  Bursaria,  on  the  other  hand,  changes  its 
direction  of  movement  only  at  longer  intervals,  and  usually  soon  ceases 
to  revolve  on  its  long  axis  as  it  turns  toward  the  aboral  side.  This  fail- 
ure to  turn  on  the  long  axis  deprives  it  of  the  great  advantage  of  being 
directed  successively  in  many  different  directions  in  the  different  planes 
of  space.  The  result  is  that  it  is  likely  to  be  destroyed  by  the  heat 
before  it  has  found  a  direction  leading  to  a  cooler  region. 


306  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

F.     Localization  of  Reactions 

A  second  factor  that  is  of  great  importance  in  making  the  move- 
ments effective  lies  in  the  proper  localization  of  the  reactions.  An 
organism  that  moves  directly  away  from  an  unfavorable  agent  (or  di- 
rectly toward  a  favorable  one)  has  a  great  advantage  over  an  organism 
whose  movements  are  not  thus  accurately  directed.  There  are  great 
differences  in  different  organisms  in  this  respect ;  some  react  very  pre- 
cisely with  reference  to  the  position  of  the  stimulating  agent,  while  others 
do  not. 

How  is  the  relation  of  the  reaction  to  the  localization  of  the  stimulus 
brought  about,  and  what  is  the  cause  of  the  differences  between  differ- 
ent organisms  in  this  respect? 

In  answering  this  question,  we  can  distinguish  three  different  classes 
of  phenomena.     These  are  the  following :  — 

(i)  First  we  have  the  simple  phenomenon  that  when  a  portion  of 
an  organism  is  stimulated  this  portion  may  respond  by  contraction,  ex- 
tension, or  other  change  of  movement.  If  the  remainder  of  the  body 
does  not  respond,  or  responds  in  a  different  way,  this  gives  at  once  a 
reaction  localized  in  a  certain  way  with  reference  to  the  place  of  stimu- 
lation. Such  local  responses  we  find  in  Amoeba,  where  the  part  strongly 
stimulated  contracts,  or  if  stimulated  by  a  food  body  it  extends.  The 
same  phenomenon  is  found  in  Hydra,  in  the  bending  of  the  body  when 
one  side  is  powerfully  stimulated,  in  the  bending  of  the  tentacles  of 
Sagartia  toward  the  point  stimulated,  and  in  the  local  contractions  of 
the  medusa  and  of  stimulated  points  on  the  body  of  the  flatworm  and 
many  other  soft-bodied  animals.  The  same  thing  is  seen  even  in  man 
when  the  electrode  of  a  battery  is  applied  directly  over  a  muscle ;  this 
muscle  now  contracts.  This  seems  a  simple  and  primitive  phenomenon, 
and  as  such  has  been  seized  upon  by  the  "tropism  theory"  and  made 
the  chief  factor  in  the  behavior  of  lower  organisms,  and  particularly  in 
all  directed  reactions.  As  we  have  shown  in  our  chapter  on  that  theory, 
this  factor  plays  by  no  means  the  extensive  part  assumed  by  the  theory, 
and  is  quite  inadequate  to  account  for  most  of  the  behavior  of  lower 
organisms.  Even  in  the  behavior  of  the  organisms  mentioned  above, 
where  it  clearly  does  play  a  part,  this  part  is  a  subordinate  one  (see 
Chapter  XIV).  In  many  organisms,  such  as  the  free  infusoria  and 
some  rotifers,  it  is  hard  to  detect  any  part  of  the  effective  behavior  that 
is  due  to  local  reaction  at  the  point  stimulated.  The  fact  that  such 
local  reactions  may  and  do  occur  in  organisms  is  of  course  a  fact  of 
much  importance,  but  taken  by  itself  it  is  utterly  inadequate  as  a  general 
explanation  of  directed  reactions. 


ANALYSIS   OF  BEHAVIOR   IN   LOWER   ORGANISMS         307 

(2)  In  many  cases  we  find  that  the  relation  of  the  movement  to 
the  source  of  stimulation  is  brought  about  indirectly  through  selec- 
tion from  among  varied  movements.  The  organism  tries  moving  in 
many  directions,  till  it  finds  one  in  which  there  is  no  stimulus  to  further 
change.  In  this  way  it  may  become  oriented  very  precisely  if  the  con- 
ditions require.  This  is  the  prevailing  method  in  the  infusoria  and  in 
various  other  organisms,  as  we  have  seen.  It  is  becoming  evident  that 
this  method  is  more  common  even  among  higher  organisms  than  has 
been  hitherto  set  forth.  Movements  of  the  head  from  side  to  side,  such 
as  we  find  in  the  flatworm  and  many  other  animals,  movements  of  the 
eyes  or  other  sense  organs,  such  as  are  common  in  higher  animals,  or 
movements  of  the  body  from  side  to  side,  as  in  the  swimming  of  many 
creatures,  give  opportunity  for  determining  which  movement  tends  to 
retain  the  stimulus,  which  to  get  rid  of  it.  In  this  way  they  form  a  basis 
for  the  determination  of  the  direction  of  locomotion  through  the  method 
of  trial.     How  much  part  such  movements  play  needs  careful  study. 

(3)  In  still  other  cases  the  reaction  shows  a  definite  relation  to  the 
localization  of  the  stimulus,  yet  it  is  not  due  to  local  reaction  of  the  part 
stimulated,  nor  is  it  brought  about  by  trial.  If  an  infusorian  is  stimu- 
lated at  the  anterior  end  it  swims  backward ;  stimulated  at  the  posterior 
end  it  swims  forward.  Both  these  movements  are  reactions  of  the 
entire  organisms,  all  the  motor  organs  of  the  body  concurring  to  pro- 
duce them;  they  are  not  produced  by  local  reactions  of  the  organs  at 
one  end  or  the  other.  The  flatworm  turns  toward  or  away  from  the  side 
stimulated,  by  reactions  involving  the  muscles  of  both  sides,  as  well  as 
transverse  and  dorso-ventral  muscles,  all  at  a  distance  from  the  point 
stimulated.  If  stimulated  on  the  upper  surface  of  the  head,  a  compli- 
cated twisting  reaction  occurs,  involving  many  sets  of  muscles  in  vari- 
ous regions  (p.  273),  by  which  the  ventral  surface  is  made  to  face  the 
stimulating  agent  (p.  236).  Innumerable  instances  of  this  class  of  reac- 
tions could  be  given;  they  include  perhaps  the  greater  number  of  the 
directed  movements  of  organisms. 

In  these  reactions  a  stimulus  at  one  side  or  end  evidently  produces  a 
different  reaction  from  a  stimulus  at  the  opposite  side  or  end,  though 
the  reaction  is  not  primarily  at  the  point  stimulated.  Doubtless  the 
stimulus  starts  a  physiological  process  of  some  sort  at  the  point  upon 
which  it  impinges,  and  this  determines  in  some  way  the  direction  in 
which  the  organism  shall  move.  This  effect  in  the  region  directly  acted 
upon  corresponds  to  the  "local  sign"  in  human  physiological  psychol- 
ogy. Behavior  thus  brought  about  is  of  course  more  effective  than  that 
of  the  two  preceding  classes,  permitting  more  direct  and  rapid  reaction 
than  the  method  of  trial,  and  meeting  the  conditions  in  an  incomparably 


308  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

more  adequate  way  than  the  simple  local  reaction  of  the  part  stimu- 
lated. 

Such  behavior  apparently  represents  not  a  primitive  condition,  but 
a  product  of  development.     How  has  it  been  brought  about? 

It  is  evident  that  the  operation  of  the  law  of  the  readier  resolution  of 
physiological  states  after  repetition,  taken  in  connection  with  behavior 
by  selection  from  varied  movements,  would  in  course  of  time  produce 
such  reactions.  Let  us  suppose  that  the  original  reaction  to  a  stimulus 
at  the  anterior  end  was  simply  the  production  of  a  change  resulting  in 
varied  movements,  according  to  the  principles  governing  the  actual 
reactions  of  Paramecium.  These  varied  movements  would  include  for- 
ward as  well  as  backward  motion.  The  forward  movement  would  in- 
duce still  further  stimulation,  hence  it  would  be  changed.  The  back- 
ward movement  would  give  relief  from  stimulation,  hence  would  not  be 
changed  (till  internal  conditions  require).  Hence  after  stimulation  at 
the  anterior  end  the  physiological  states  induced  will  always  be  resolved 
finally  into  that  state  corresponding  to  backward  movement.  This 
resolution  will  in  time  become  spontaneous ;  the  physiological  state  due 
to  stimulation  at  the  anterior  end  will  pass  at  once  into  that  producing 
movement  backward.  Trial  movements  will  no  longer  occur,  but  the 
organism  will  respond  at  once  by  backward  motion.  A  similar  exposi- 
tion will  account,  mutatis  mutandis,  for  other  localized  reactions. 

Whether  this  condition  has  been  brought  in  the  way  above  sketched 
or  not,  its  existence  is  evidently  a  fact- of  great  importance.  It  is  a  step 
forward  from  the  pure  "trial  movement"  condition.  Wherever  the  or- 
ganism can  react  in  this  manner,  and  this  will  meet  the  conditions 
equally  well,  we  may  expect  such  behavior  in  place  of  repeated  trials. 
In  higher  organisms  especially  we  find  this  behavior  playing  a  large  part. 
Such  organisms  could  not  be  expected,  for  example,  to  orient  to  gravity 
or  to  light  rays  by  trial  movements,  as  the  infusoria  do,  but  rather  to 
turn  directly  toward  or  from  the  source  of  action  of  the  stimulating 
agent.     This  is,  of  course,  known  in  many  cases  to  be  true. 

But  under  many  circumstances  the  reaction  by  trial  is  surer,  though 
less  rapid,  than  that  depending  directly  on  the  localization  of  the  stimu- 
lus, so  that  we  find  the  trial  method  much  used  even  by  higher  organ- 
isms (see  Chapter  XII).  Further,  the  more  direct  reactions  due  to  pre- 
cise localization  are  again  combined  as  elementary  factors  to  produce 
behavior  based  on  the  method  of  trial,  as  when  the  flatworm  turns  toward 
and  "tries"  any  source  of  weak  stimulation,  accepting  or  rejecting  it 
finally,  according  as  it  proves  fit  for  food  or  not.  Thus  we  have  be- 
havior rising  to  a  higher  degree  of  complexity,  —  the  method  of  trial  in 
the  second  or  third  degree,  as  it  were.  Examples  of  this  character  are 
abundant. 


ANALYSIS  OF  BEHAVIOR  IN  LOWER   ORGANISMS         309 
G.     Positive  Reactions 

We  have  thus  far  dealt  primarily  with  reactions  to  environmental 
conditions  that  interfere  with  the  normal  life  processes.  We  find  that 
these  induce  changes  in  behavior,  subjecting  the  organism  to  new  con- 
ditions, the  more  favorable  one  of  which  is  selected.  This  gives  us  a 
basis  for  the  understanding  of  reactions  toward  conditions  which  favor 
the  normal  life  processes,  —  that  is,  positive  reactions. 

In  conditions  that  are  completely  favorable  —  so  that  all  the  life 
processes  are  taking  place  without  lack  or  hindrance  —  there  is  of 
course  no  need  for  a  change  in  behavior,  for  definite  reactions  of  any 
sort.  The  most  natural  behavior  on  reaching  such  conditions,  and  that 
which  is  actually  found  as  a  general  rule  among  lower  organisms,  is  a 
continuation  of  the  activities  already  in  progress.  These  activities  have 
resulted  in  favorable  conditions,  hence  it  is  natural  to  keep  them  up ; 
there  is  no  cause  for  a  change.  This  we  find  strikingly  exemplified  in 
bacteria,  infusoria,  rotifers,  and  many  other  organisms  under  most 
classes  of  stimuli.  A  change  in  behavior  takes  place  only  when  the  ac- 
tivities tend  to  remove  the  organism  from  the  favorable  conditions. 
Unfavorable  conditions  cause  a  change  in  behavior;  favorable  condi- 
tions cause  none.  It  is  perhaps  a  general  rule  in  organisms,  high  or 
low,  that  continued  completely  favorable  conditions  do  not  lead  to  defi- 
nite reactions.  Of  course  while  the  external  conditions  remain  the  same, 
the  internal  processes  may  change  in  such  a  way  that  these  conditions 
are  no  longer  favorable,  and  now  the  behavior  may  change. 

But  when  the  organism  is  not  completely  enveloped  by  favorable 
conditions,  but  is  on  the  boundary,  if  we  may  so  express  it,  between  favor- 
able and  unfavorable  ones,  then  there  is  often  a  definite  change  in  the 
behavior  leading  toward  the  favorable  conditions,  —  a  positive  reaction. 
To  understand  such  reactions,  we  may  start  from  the  fact  that  unfavor- 
able internal  conditions  (as  well  as  external  ones)  cause  a  change  of 
behavior.  The  Hydra  or  sea  anemone  whose  metabolic  processes  are 
interfered  with  by  lack  of  material,  exchanges  its  usual  behavior  for 
activities  of  a  totally  different  character,  setting  forth  on  a  tour  of  ex- 
ploration. It  is  a  general  fact  that  the  hungry  animal  sets  in  operation 
trains  of  activity  differing  from  the  usual  ones.  Interference  with  respi- 
ration or  with  other  internal  processes  has  similar  effects.  An  increase 
of  temperature  above  that  favorable  for  the  physiological  processes  like- 
wise starts  violent  activities.  Indeed,  it  is  a  general  rule  that  changes 
of  internal  condition  unfavorable  to  the  physiological  processes  set  in 
operation  marked  changes  in  behavior. 

But  the  activities  thus  induced  are  in  themselves  undirected,  save 


310  BEHAVIOR   OF    THE  LOWER   ORGANISMS 

by  structural  conditions.  There  is  nothing  in  the  cause  that  produces 
them,  taken  by  itself,  to  specifically  direct  them  with  reference  to  exter- 
nal things.  Let  us  suppose,  however,  that  certain  of  these  movements 
lead  to  a  condition  which  relieves  the  interference  with  the  internal 
processes.  The  cause  for  a  change  of  behavior  is  now  removed,  hence 
the  organism  continues  its  present  movement  —  continues  in  the  direc- 
tion, we  will  say,  that  has  led  to  the  favorable  conditions.  But  perhaps 
later  —  sometimes  at  the  very  next  instant  —  this  same  movement  may 
tend  to  remove  the  organism  from  the  favorable  conditions  —  as  when 
a  heated  Paramecium  passes  across  a  small  area  of  cool  water,  or  a  hun- 
gry organism  comes  against  food.  Thereupon  the  cause  for  a  change  — 
interference  with  the  life  processes  —  is  again  set  in  operation,  and  this 
movement  changes  to  another.  Thus  the  animal  changes  all  behavior 
that  leads  away  from  the  favorable  condition,  and  continues  that  which 
tends  to  retain  it,  so  that  we  get  what  we  call  a  positive  reaction.  The 
change  of  behavior  is  due  primarily  in  each  case  to  the  unfavorable 
condition,  internal  or  external  —  perhaps  in  last  analysis  always  in- 
ternal. 

Behavior  of  this  character  is  seen  with  diagrammatic  clearness  in 
the  free-swimming  infusoria.  These  animals  continue  their  movements 
so  long  as  they  lead  to  favorable  conditions,  changing  at  once  such  move- 
ments as  lead  away.  They  thus  retain  favorable  conditions  by  avoiding 
unfavorable  ones;  the  positive  reaction  is  seen  to  be  a  secondary  result 
of  negative  ones. 

In  the  infusoria  we  have  then  the  most  elementary  condition  of  the 
positive  reaction.  Let  us  now  examine  a  more  pronounced  type  of 
positive  reaction,  —  movement  directly  toward  the  favorable  condition. 
Amoeba  flows  toward  and  follows  a  food  body  with  which  it  comes  in 
contact,  as  illustrated  in  Fig.  19,  p.  14.  Take,  for  example,  its  action 
at  3  in  this  figure.  It  moves  forward  with  broad  front,  part  of  the 
movement  taking  it  toward  the  food,  part  away.  On  coming  in  contact 
with  the  food,  all  movement  is  changed  which  takes  it  away,  only  that 
being  retained  which  keeps  the  animal  in  contact  with  the  food.  We 
have  here  then,  as  in  infusoria,  a  case  of  selection  from  varied  movements, 
the  central  point  being  the  changing  of  all  motion  that  leads  to  less  favor- 
able conditions. 

This  is,  perhaps,  the  fundamental  condition  of  affairs,  from  which 
all  positive  reactions  are  derived.  The  animal  moves  (partly  or  entirely 
from  internal  impulse,  as  we  have  seen),  but  changes  all  movements  that 
lead  to  less  favorable  conditions.  It  therefore  moves  toward  the  favor- 
able conditions.  In  many  higher  animals,  even,  this  behavior  is  seen 
in  the  random  movements  by  which  food  is  sought,  by  the  aid  of  the 


ANALYSIS  OF  BEHAVIOR  IN   LOWER   ORGANISMS         311 

chemical  stimulation  which  it  sends  forth.  The  movements  leading  to 
loss  of  the  favorable  stimulation  are  changed,  the  others  continued, 
till  the  food  is  found  (see  p.  247). 

But  many  animals  have  developed,  in  some  way,  as  we  have  seen  in 
the  account  of  the  negative  reactions,  the  power  of  localizing  their  reac- 
tions precisely,  so  as  to  move  in  a  certain  definite  way  with  relation  to 
the  position  of  the  source  of  stimulation.  Let  us  suppose  that  such  an 
organism  is  reached  by  a  favorable  stimulus  on  one  side  —  food,  or  the 
optimum  temperature.  It  has  the  power  of  turning  directly  toward  this 
favorable  condition  —  and  this,  of  course,  is  what  happens  in  many 
higher  organisms.  There  is  the  same  reason  to  think  that  this  condition 
is  not  primitive  that  we  saw  in  the  case  of  negative  reactions.  It  may, 
perhaps,  be  conceived  as  derived  from  behavior  through  selection  of 
overproduced  movements  in  the  way  set  forth  on  page  308.  The  precise 
reactions  shown  in  the  actual  taking  of  food  are  perhaps  derivable  in 
the  same  way. 

In  those  animals  whose  positive  reactions  are  precisely  defined  and 
localized,  there  is,  of  course,  the  same  evidence  that  the  impulse  to  change 
of  behavior  comes  from  within  and  is  due  to  lack  or  hindrance  of  the 
physiological  processes,  that  we  find  elsewhere.  If  the  metabolic  pro- 
cesses lack  material  for  proper  action,  the  medusa  or  sea  anemone 
changes  its  behavior  and  moves  about,  even  though  there  is  nothing 
present  to  which  it  can  react  positively.  When  some  object  is  reached, 
whether  there  shall  be  a  positive  reaction  or  not  depends  again  on  the 
state  of  the  metabolic  processes.  If  their  state  is  bad,  the  animal  re- 
acts positively  to  almost  anything;  if  fair,  the  animal  reacts  positively 
to  substances  that  will  improve  them ;  if  they  are  in  a  completely  satis- 
factory condition,  the  animal  does  not  react  positively  even  to  good 
food. 

Thus  with  all  conditions  absolutely  favorable  there  will  be  no  reac- 
tion, either  positive  or  negative.  At  the  boundary  between  favorable 
and  unfavorable  conditions,  the  animal  moves  in  such  a  way  as  to  retain 
the  favorable  conditions.  This  is  primitively  due  to  selection  from 
varied  movements  —  all  movement  leading  to  less  favorable  conditions 
being  changed.  The  "negative  reactions"  thus  seem  to  furnish  in  a 
certain  sense  the  primitive  building  stones  from  which  the  derived  posi- 
tive reactions  are  constructed.  By  development  of  the  power  of  precise 
localization  of  reactions,  the  derivation  of  the  positive  reaction  in  this 
manner  is  in  higher  animals  obscured.  The  fundamental  fact  for  both 
positive  and  negative  reactions  is  that  interference  with  the  physiological 
processes  of  the  organism  causes  a  change  of  behavior. 


312  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

3.     Resume  of  the  Fundamental  Features  of  Behavior 

We  have  considered  in  the  three  foregoing  chapters,  first  the  deter- 
mining factors  of  movements,  and  second  the  movements  themselves. 
Let  us  now  attempt  to  put  together  the  most  important  points  in  both, 
so  as  to  reach  a  general  characterization  of  behavior. 

The  three  most  significant  features  of  behavior  appear  to  be  (1)  the 
determination  of  the  nature  of  reactions  by  the  relation  of  external 
conditions  to  the  internal  physiological  processes,  and  particularly  the 
general  principle  that  interference  with  these  processes  causes  a  change 
in  behavior;  (2)  reaction  by  varied  or  overproduced  movements,  with 
selection  from  the  varied  conditions  resulting  from  these  movements  — 
or,  in  brief,  reaction  by  selection  of  overproduced  movements;  (3)  the 
law  of  the  readier  resolution  of  physiological  states  after  repetition.  The 
first  of  these  phenomena  produces  the  regulatory  character  of  behavior. 
The  second  and  third  furnish  the  mainsprings  for  the  development  of 
behavior,  the  second  being  constructive,  the  third  conservative. 

The  activity  of  organisms  we  found  to  be  spontaneous,  in  the  sense 
that  it  is  due  to  internal  energy,  which  may  be  set  in  operation  and  even 
changed  in  its  action  without  present  external  stimuli.  In  reactions 
this  energy  is  merely  released  by  present  external  stimuli.  What  form 
the  activity  shall  take  is  limited  by  the  action  system,  and  within  these 
limits  is  determined  by  the  physiological  state  of  the  organism.  Physio- 
logical states  depend  on  many  factors.  The  two  primary  classes  of 
states  depend  on  whether  the  internal  life  processes  are  proceeding  unin- 
terruptedly in  the  usual  way.  Interference  with  these  processes  produces 
a  physiological  state  of  a  certain  character  ("negative"),  while  release 
from  interference  or  assistance  to  those  processes  produces  a  different 
state  ("positive").  Within  or  beside  these  contrasted  primary  classes, 
many  subsidiary  variations  of  physiological  condition  are  possible,  each 
with  its  corresponding  method  of  behavior ;  at  least  five  of  these  have  been 
distinguished  in  a  unicellular  organism.  Any  change,  external  or  in- 
ternal, may  modify  the  physiological  state,  and  hence  the  behavior. 

The  effects  of  external  agents  depends  largely  on  their  relation  to  the 
normal  course  of  the  life  processes  —  whether  aiding  or  interfering, 
or  neither.  A  primary  fact  is  that  interference  with  the  life  processes 
produces  progressive  changes  in  physiological  state,  inducing  repeated 
changes  in  behavior.  This  is  in  itself  regulatory,  tending  to  relieve  the 
interference,  whether  due  to  internal  or  external  causes;  it  is  a  process 
of  finding  a  reaction  fitted  to  produce  a  more  favorable  condition.  When 
through  such  changes  a  fitting  reaction  is  found,  the  changes  in  physio- 
logical state  and  hence  of  behavior  cease,  since  there  is  no  further  cause 


ANALYSIS  OF  BEHAVIOR  IN   LOWER   ORGANISMS         313 

for  change.  In  the  same  way  a  fitting  reaction  to  a  beneficial  change, 
or  one  releasing  from  interference,  may  be  found.  This  fitting  reaction 
then  tends  to  be  preserved,  by  the  law  of  the  resolution  of  physiological 
states,  in  accordance  with  which  the  physiological  state  inducing  this 
reaction  is  reached  more  readily  after  repetition.  Thus  the  production 
of  varied  movements  by  stimulation  is  the  progressive  factor  in  behavior, 
while  the  law  of  the  resolution  of  physiological  states  is  the  conservative 
factor,  tending  to  retain  fitting  reactions  once  attained. 

Through  the  law  of  the  resolution  of  physiological  states  behavior 
tends  to  pass  from  the  pure  "trial"  condition  to  a  more  defined  state. 
The  operation  of  this  law  tends  to  produce  reactions  precisely  localized 
with  reference  to  the  position  of  the  stimulating  agent ;  increased  appro- 
priate reaction  to  the  first  weak  effects  of  injurious  or  beneficial  stimuli ; 
and  appropriate  reactions  to  representative  stimuli,  according  as  they 
are  followed  by  injurious  or  beneficial  stimuli.  In  higher  organisms 
such  defining  of  the  reactions  has  gone  far ;  much  of  the  behavior  con- 
sists of  derived  reactions.  There  are  in  such  organisms  doubtless  other 
factors  producing  derived  reactions,  besides  the  law  just  mentioned. 
These  are  treated  in  our  chapter  on  the  "Development  of  Behavior." 

Thus  through  the  production  of  varied  movements  by  stimulation 
the  organism  finds  the  best  method  of  behavior,  and  through  the  law 
of  the  resolution  of  physiological  states  it  tends  to  retain  this  method 
as  long  as  it  is  the  best  method.  Through  the  same  process  it  of  course 
tends  to  lose  this  method  when  it  is  no  longer  adapted  to  the  conditions. 
Thus  behavior  is  regulatory  in  essential  character;  it  is  the  process  by 
which  the  organism  tends  to  find  conditions  favorable  to  its  life  processes 
and  to  retain  them,  and  it  contains  within  itself  the  conditions  for  its 
own  more  efficient  development. 


CHAPTER  XIX 
DEVELOPMENT   OF   BEHAVIOR 

It  is  not  the  primary  purpose  of  the  present  work  to  treat  the  problems 
of  development,  but  rather  to  give  an  analysis  of  behavior  as  we  now  find 
it.  But  the  results  of  this  analysis  furnish  a  certain  amount  of  evidence 
as  to  how  development  may  have  occurred;  this  it  will  be  well  to  set 
forth  briefly.  We  shall  consider  first  the  development  of  behavior  in 
the  individual,  then  its  development  in  the  race.  In  unicellular  organ- 
isms the  first,  perhaps,  includes  the  second. 

The  primary  facts  for  development  in  behavior  are  two  principles 
to  which  our  analysis  of  the  chief  factors  in  behavior  have  led  us.  One 
of  these  is  that  behavior  is  based  fundamentally  on  the  selection  of  varied 
movements.  The  other  is  the  law  in  accordance  with  which  the  resolu- 
tion of  one  physiological  state  into  another  becomes  readier  and  more 
rapid  through  repetition. 

In  making  use  of  the  law  of  the  readier  resolution  of  physiological 
states  after  repetition  in  the  study  of  development,  it  needs  to  be  kept 
in  mind  that  this  law  has  been  rigidly  demonstrated  for  the  lower  organ- 
isms only  in  scattered  instances.  It  has  been  shown  to  be  valid  in  cer- 
tain unicellular  organisms,  but  in  these  cases  it  has  not  been  shown  that 
the  modifications  induced  are  lasting,  as  must  be  the  case  if  this  law  plays 
a  part  in  the  development  of  behavior.  In  the  lowest  metazoa  the  law 
has  likewise  been  demonstrated  only  for  a  few  cases.  In  the  flatworm 
and  the  Crustacea  we  find  the  law  clearly  exhibited  in  the  form  that  is 
necessary  in  order  that  it  may  play  a  part  in  the  permanent  modification 
of  behavior. 

On  the  other  hand,  the  fact  that  the  law  remains  undemonstrated 
for  many  of  the  lowest  organisms  by  no  means  indicates  that  it  is  not  here 
valid.  We  lack  proper  experiments  to  show  whether  it  exists  or  not. 
It  is  exceedingly  difficult  to  carry  out  experiments  that  shall  actually 
test  this  matter  in  the  lowest  animals.  The  view  that  this  law  is  univer- 
sally valid  in  organic  behavior  is  thoroughly  consistent  with  all  that  we 
know  of  the  behavior  of  lower  organisms,  and  the  fact  that  it  has  actually 
been  demonstrated  in  certain  cases  favorable  for  experimentation  in 
unicellular  organisms  raises  a  presumption  of  its  general  validity.     The 

314 


DEVELOPMENT  OF  BEHAVIOR  315 

following  discussion  of  development  is  based  on  the  assumption  that  the 
law  is  one  of  general  validity.  It  must  be  kept  in  mind  that  this  is 
partly  an  assumption,  but  the  probability  that  this  will  be  found  true 
is  such  that  the  relation  of  development  to  the  law  is  worth  setting  forth. 
There  is  no  other  need  greater  in  the  study  of  animal  behavior  than 
that  of  a  thorough  investigation  of  the  validity  of  this  law  in  the  lower 
organisms. 

The  question  in  which  we  are  here  interested  is  then  the  following : 
How  can  behavior  develop  ?  That  is,  how  can  it  change  so  as  to  become 
more  effective  —  more  regulatory  ? 

(1)  The  behavior  of  any  organism  may  become  more  effective 
through  an  increased  tendency  for  the  first  weak  effects  of  injurious  or 
beneficial  agents  to  cause  the  appropriate  reaction ;  in  other  words, 
through  increased  delicacy  of  perception  and  discrimination  on  the  part 
of  the  organism.  Such  a  change  would  be  brought  about  through  the 
law  of  the  readier  resolution  of  physiological  states  after  repetition. 
When  the  organism  is  subjected  to  a  slight  stimulus,  this  changes  its 
physiological  state,  though  perhaps  not  sufficiently  to  cause  a  reaction. 
Such  a  slight  stimulus  would  be  produced  by  a  very  weak  solution  of  a 
chemical,  or  by  a  slight  increase  in  temperature.  Now,  suppose  that 
this  weak  stimulus,  causing  no  reaction,  is  regularly  followed  by  a 
stronger  one,  as  would  be  the  case  if  the  weak  chemical  or  slight  warmth 
were  the  outer  boundary  of  a  strong  chemical  solution,  or  of  a  region 
of  high  temperature  toward  which  the  organism  is  moving.  This 
stronger  stimulus  would  produce  an  intense  physiological  state,  corre- 
sponding to  a  marked  negative  reaction.  That  is,  the  first  (weak) 
physiological  state  is  regularly  resolved  by  the  action  of  the  stimulating 
agent  into  the  second  (intense)  one,  inducing  reaction.  In  time  the 
first  state  would  come  to  resolve  itself  into  the  second  one  even  before 
the  intense  stimulus  had  come  into  action.  As  a  result,  the  organism 
would  react  now  to  the  weak  stimulus,  as  it  had  before  reacted  only  to 
the  strong  one.  It  would  thus  be  prevented  from  entering  the  region 
of  the  chemical  or  the  heat,  even  before  any  injury  had  arisen. 

(2)  In  the  same  way  the  organism  may  come  to  react  positively  or 
negatively  to  a  stimulus  that  is  in  itself  not  beneficial  nor  injurious,  but 
which  serves  as  a  sign  of  a  beneficial  or  injurious  agent,  because  it  regu- 
larly precedes  such  an  agent.  Suppose  that  a  slight  decrease  in  illumina- 
tion (a  shadow),  which  is  of  itself  indifferent,  regularly  precedes  the  ap- 
proach of  an  enemy,  as  happens  in  the  sea  urchin.  The  slight  decrease 
in  light  induces  a  certain  physiological  state,  which  is  so  little  marked 
that  in  itself  it  produces  no  reaction.  But  through  the  immediately 
following  attack  of  the  enemy,  this  indifferent  physiological  state  is 


316 


BEHAVIOR  OF   THE  LOWER   ORGANISMS 


regularly  resolved  into  an  intense  one,  corresponding  to  a  strong  negative 
reaction.  Then  after  many  repetitions  of  this  process  the  indifferent 
state  resolves  itself  at  once  into  the  intense  one,  and  the  animal  reacts 
at  the  change  in  illumination,  before  the  enemy  has  reached  it.  This 
tendency  to  react  to  "representative"  factors,  rather  than  to  those 
which  are  in  themselves  beneficial  or  injurious,  is,  of  course,  immensely 
developed  in  higher  animals.  All  positive  or  negative  reactions  to  things 
merely  seen  or  heard,  which  are  not  directly  beneficial  or  injurious  save 
when  brought  into  direct  contact  with  the  organism,  are,  of  course,  reac- 
tions to  such  representative  stimuli. 

It  is  clear  that  neither  the  tendency  to  react  to  faint  stimuli,  nor  that 
to  react  to  "representative"  factors  will  be  increased,  save  as  this  is 
required  by  the  environment.  If  the  indifferent  stimulus  is  not  followed 
with  some  regularity  by  the  powerful  one ;  that  is,  if  it  does  not  really 
introduce  a  powerful  agent,  then  there  will  be  no  tendency  for  the  or- 
ganism to  acquire  a  reaction  to  this  indifferent  stimulus,  for  there  will 
be  no  regular  resolution  of  the  first  (faint)  physiological  change  into  the 
second  (intense)  one.  And  of  course  it  would  be  no  advantage,  but  on  the 
co'ntrary  a  positive  disadvantage,  for  the  organism  to  acquire  tins  ten- 
dency to  react  to  all  weak  stimuli.  If  it  reacted  negatively  to  every  slight 
change  in  the  environment,  its  movements  would  be  seriously  impeded ; 
continued  locomotion  in  any  one  direction  would  be  almost  impossible, 
and  its  activity  would  be  frittered  away  in  useless  and  disconnected  reac- 
tions. The  behavior  becomes  modified,  in  accordance  with  the  prin- 
ciples above  set  forth,  only  as  it  is  to  the  advantage  of  the  organism  that 
it  should  be  so  modified;  that  is,  only  as  the  modification  favors  the 
normal  current  of  life  activities. 

(3)  Progress  takes  place  through  increase  in  the  complexity  and 
permanence  of  physiological  states,  and  in  the  tendency  to  react  to  these 
derived  and  complex  states,  instead  of  to  the  primitive  and  simple  ones. 
We  may  imagine  an  organism  whose  physiological  state  depends  entirely 
on  the  stimulus  now  acting  upon  it,  the  organism  returning  completely, 
as  soon  as  the  stimulus  ceases,  to  its  original  state.  Such  an  organism 
could  react  only  with  relation  to  the  present  stimulus,  and  its  reaction  to 
the  same  stimulus  would  always  be  the  same.  We  might  even  imagine  an 
organism  that  could  change  in  only  one  way  under  the  action  of  stimuli ; 
its  reactions  to  all  stimuli  would  be  the  same.  Such  organisms  would 
represent  a  purely  reflex  type  of  behavior.  An  advance  on  this  condi- 
tion would  be  represented  by  cases  where  the  physiological  state  induced 
by  a  stimulus  endures  for  a  short  time,  influencing  the  immediately 
succeeding  reactions,  and  a  further  advance  when  the  reaction  performed 
by  the  organism  influences  its  physiological  state,  and  therefore  its  later 


DEVELOPMENT  OF  BEHAVIOR  317 

reactions.  Other  advances  would  come  in  the  production  of  different 
physiological  states  according  to  the  different  organs  or  parts  of  the  body 
stimulated;  this  condition  would  naturally  arise  as  structural  differen- 
tiations were  developed  in  the  body.  As  new  organs  develop  and  the 
body  becomes  more  complex,  each  part  will  naturally  have  physiological 
states  peculiar  to  itself,  and  will  be  acted  upon  by  external  stimuli, 
producing  changes  in  its  physiological  states.  This  is  evidently  the  case 
in  such  organisms  as  the  sea  urchin  and  sea  anemone.  These  partial 
physiological  states  of  the  different  organs  will  then  interact,  altering 
each  other  and  combining  to  form  a  general  state  for  the  entire  organism. 
All  the  partial  physiological  states  will  be  regulated,  as  in  the  separate 
organism,  bv  their  relation  to  the  normal  life  current  of  the  organ  con- 
cerned,  and  further,  their  combinations  will  be  regulated  by  their  rela- 
tion to  the  general  life  current  of  the  organism.  Whatever  interferes 
with  this  normal  life  current  will  be  changed,  while  that  which  does 
not  interfere  must  persist.  The  partial  and  general  physiological 
states  will  be  subject  to  the  laws  of  the  combination  and  regulation  of 
physiological  states,  just  as  in  simple  organisms.  They  will  tend  to 
discharge  themselves  in  action,  or  by  resolution  into  other  states,  as  in 
the  simple  organisms.  Thus  the  behavior  of  the  organism  must  become 
in  time  controlled  by  these  physiological  states,  derived  from  many 
sources  besides  that  of  the  present  stimulus.  Behavior  is  gradually 
emancipated  from  its  bondage  to  present  external  conditions,  and  de- 
pends largely  upon  the  past  experience  and  present  needs  of  the  organism. 
This  is  the  condition  we  find  in  higher  animals,  and  especially  in  man. 

The  various  stages  set  forth  above  are  merely  logical  divisions,  and 
probably  do  not  correspond  in  any  close  way  to  actual  stages  in  the  de- 
velopment of  behavior.  There  seems  to  be  no  reason  to  suppose  that 
an  organism  ever  existed  in  which  the  original  state  is  immediately 
restored  on  the  cessation  of  a  stimulus.  This  immediate  return  to  the 
original  state  is  not  what  we  should  expect  from  analogy  even  with  inor- 
ganic substances.1  Even  in  unicellular  organisms  we  find  a  consider- 
able complication  of  physiological  states,  depending  on  past  stimuli, 
past  reactions,  localization  of  the  stimulus,  and  present  external  condi- 
tions, as  well  doubtless  as  upon  other  factors. 

Progress  along  the  line  just  set  forth  will  be  brought  about  by  the 
same  factors,  whatever  they  may  be,  that  determine  the  development 

1  With  relation  to  colloids,  the  substances  of  which  organisms  are  mainly  composed, 
a  high  authority  in  physical  chemistry  remarks  as  follows:  "Their  qualities  often 
depend  in  the  clearest  way  upon  the  former  history  of  the  colloid,  its  age,  its  previous 
temperature,  and  the  time  this  continued :  in  short,  on  the  way  it  has  reached  its  present 
condition "  (Bredig,  1902,  p.  183).  The  facts  of  behavior  in  organisms  might  be  cited 
as  illustrations  of  this  statement. 


318  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

of  complexity  in  structure.  Differentiation  of  structure  and  of  physio- 
logical states  must  go  hand  in  hand.  It  is  not  our  province  to  attempt 
to  account  for  structural  differentiations.  The  problem  is  the  general 
problem  of  evolution. 

(4)  Progress  in  behavior  may  take  place  through  increased  variety 
and  precision  of  the  movements  brought  about  by  stimulation.  Certain 
kinds  of  movements  are  much  better  adapted  to  relieving  an  organism 
from  an  unfavorable  stimulation  or  securing  it  a  favorable  one  than  are 
others.  This  is  illustrated  by  a  comparison  of  the  reactions  of  Amoeba 
and  Paramecium,  or  of  the  reaction  of  Bursaria  to  heat  with  that 
of  Paramecium,  as  set  forth  on  page  305.  Owing  to  the  difference  in 
the  effectiveness  of  their  movements,  if  an  area  containing  equal  num- 
bers of  Paramecia  and  Bursaria  is  heated  at  one  end,  many  of  the 
Bursariae  are  killed,  while  all  the  Paramecia  escape. 

.  New  and  better  adapted  methods  of  movement  may  be  acquired 
through  the  selection  of  varied  movements,  in  conjunction  with  the 
law  of  the  resolution  of  physiological  states.  Under  strong  stimula- 
tion the  organism,  as  it  passes  from  one  physiological  state  to  another, 
tries  successively  all  the  movements  of  which  it  is  capable.  One  of 
these  movements  (the  spiral  course,  in  the  case  of  Bursaria)  finally 
removes  the  organism  from  the  stimulating  agent.  This  happens  every 
time  the  organism  is  stimulated  in  this  manner.  The  result  is  that  each 
physiological  state  is  resolved  into  the  succeeding  one,  until  that  one  is 
reached  in  which  the  organism  responds  by  the  effectual  movement. 
After  a  number  of  repetitions,  this  resolution  takes  place  immediately, 
in  accordance  with  the  law  that  after  repeated  resolutions  of  one  physio- 
logical state  into  another,  this  resolution  takes  place  spontaneously  and 
rapidly.  Thus  the  organism  responds  at  once  with  the  effectual  move- 
ment, and  escapes. 

In  the  same  way  the  use  of  new  organs  might  be  acquired.  Suppose 
that  an  Amoeba  sends  forth,  as  sometimes  happens,  a  long,  slender  pseu- 
dopodium,  which  may  vibrate  back  and  forth,  like  a  flagellum.  When 
stimulated,  the  overproduced  movements  of  the  organism,  as  it  passes 
from  one  physiological  state  to  another,  include  the  vibration  of  this 
pseudopodium.  Suppose  that  by  this  vibration  the  Amceba  is  at  once 
moved  away  from  the  stimulating  agent  —  the  pseudopodium  acting  as 
does  the  flagellum  in  Euglena.  If  this  is  repeated,  the  physiological  state 
inducing  other  movements  will  always  be  resolved  finally  into  that  induc- 
ing this  one,  and  in  time  this  resolution  will  take  place  so  rapidly  that 
only  this  movement  will  come  to  actuality.  The  Amoeba  will  have  ac- 
quired the  habit  when  stimulated  of  swimming  by  means  of  a  flagellum. 
Thus    the  behavior  of  organisms  is  of  such  a  character  as  to  pro- 


DEVELOPMENT   OF  BEHAVIOR  319 

vide  for  its  own  development.  Through  the  principle  of  the  production 
of  varied  movements,  and  that  of  the  resolution  of  one  physiological 
state  into  another,  anything  that  is  possible  is  tried,  and  anything  that 
turns  out  to  be  advantageous  to  the  organism  is  held  and  made  permanent. 

Thus  through  development  in  accordance  with  the  two  principles 
mentioned,  the  organism  comes  to  react  no  longer  by  trial, — by  the  over- 
production of  movements, — but  by  a  single  fixed  response,  appropriate 
to  the  occasion.  This  is,  of  course,  a  great  advantage,  so  long  as  the 
conditions  remain  such  as  to  make  the  response  appropriate.  Such 
fixed  responses  are  the  general  rule  in  the  adult  behavior  of  higher  or- 
ganisms, and  are  found  to  a  certain  extent  in  all  organisms.  In  the 
higher  organisms  we  speak  of  some  of  these  fixed  responses  as  reflexes, 
tropisms,  habits,  and  instincts.  The  methods  which  we  have  discussed 
are  not  the  only  possibilities  for  the  development  of  such  responses  ;  other 
methods  we  shall  take  up  later. 

After  the  responses  of  the  organism  have  become  fixed,  conditions 
may  so  change  that  these  responses  are  no  longer  appropriate.  The 
organism  is  then  in  a  less  advantageous  position  than  one  whose  behavior 
is  determined  more  purely  by  trial  movements.  There  will  be  now  a 
tendency  for  the  fixed  responses  to  become  broken  up  and  for  processes 
of  trial  to  supplant  them,  until  new  fixed  responses,  appropriate  to  present 
conditions,  are  produced.  But  in  many  cases  the  fixed  responses  are 
so  firmly  established  as  not  to  give  way  save  after  long  experience  of 
their  lack  of  efficiency,  and  often  the  organism  is  destroyed  by  the  new 
environment,  before  it  has  developed  appropriate  responses  by  which 
to  preserve  itself. 

(5)  We  have  thus  far  considered  primarily  the  methods  by  which 
the  behavior  of  a  given  individual  may  be  modified  and  made  more 
effective.  It  needs  to  be  recalled  that  differences  between  the  behavior 
of  different  individuals  may  appear  from  other  reasons.  There  are 
congenital  variations  among  different  organisms.  Some  have  naturally 
a  greater  delicacy  of  perception  or  discrimination  than  others.  Some 
move  more  rapidly  or  in  more  or  less  varied  ways  than  others,  giving 
some  a  more  efficient  method  of  reaction  without  any  modification 
through  experience.  These  congenital  variations  play  a  most  important 
part  in  the  question  next  to  be  considered. 

(6)  Our  discussion  thus  far  has  related  to  individuals.  The  further 
question  arises  as  to  how  modifications  of  behavior  may  arise  in  the  race 
as  a  whole.  How  does  it  happen  that  the  behavior  of  the  race  becomes 
changed  in  the  same  way  as  that  of  the  individual,  so  that  succeeding 
generations  show  the  new  method  of  reacting  without  acquiring  it  for 
themselves  ? 


320  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

There  seems  to  be  no  question  but  that  the  power  of  new  individuals 
to  react  in  certain  ways  without  preliminary  trial  has  been  much  over- 
estimated. In  most  organisms  there  is  in  the  early  stages  of  develop- 
ment a  continued  process  of  trial,  through  which  the  habits  become 
established.  On  the  other  hand,  there  is  no  doubt  that  individuals  do 
appear  with  certain  ways  of  reacting  which  most  of  their  early  ancestors 
did  not  at  the  beginning  have.  The  question  as  to  how  this  happens, 
therefore,  presses  for  an  answer. 

The  answer  formerly  given  was,  that  the  acquirements  of  the  parent 
are  directly  inherited  by  the  offspring.  The  parent  having  come  to 
react  in  a  certain  way,  the  condition  of  the  system  inducing  this  reaction 
is  passed  on  to  posterity.  In  the  unicellular  organisms  there  seems  to 
be  nothing  in  the  way  of  this  inheritance  by  the  offspring  of  the  reaction 
methods  acquired  by  the  parent.  There  is  no  distinction  between  germ 
cells  and  body  cells  in  these  organisms;  all  acquirements  pertain  to  the 
reproductive  cells.  Through  reproduction  by  division  the  offspring 
are  the  parents,  merely  divided,  and  there  is  no  evident  reason  why  they 
should  not  retain  the  characteristics  of  the  parents,  however  these  char- 
acteristics were  attained.  If  this  is  the  real  state  of  the  case,  then  in 
unicellular  organisms  the  life  of  the  race  is  a  direct  continuation  of  the 
life  of  the  individuals,  and  any  acquirements  made  by  the  individuals 
are  preserved  to  the  race. 

But  in  multicellular  organisms  the  facts  show  that  in  the  immense 
majority  of  cases  the  inheritance  of  the  acquirements  of  the  parents  by 
the  offspring  does  not  occur.  We  know  that  we  do  not  start  with  the 
education  acquired  by  our  parents,  but  must  begin  at  the  bottom,  and 
acquire  both  knowledge  and  wisdom  of  action.  In  other  words,  we 
know  that  we  fail  to  inherit  directly  the  more  efficient  methods  of  reac- 
tion acquired  through  experience  by  our  parents,  in  at  least  nine  hundred 
and  ninety-nine  cases  out  of  a  thousand.  Moreover,  the  theoretical 
difficulties  in  the  way  of  such  inheritance  are  great,  and  no  demonstrative 
evidence  seems  to  exist  that  it  ever  occurs.  Thus  we  are  certain  that  in 
most  cases  it  does  not  take  place,  and  must  doubt  whether  it  is  possible. 

If  we  give  up,  as  most  students  of  heredity  do,  the  inheritance  of  ac- 
quired characters,  the  alternative  explanation  for  progress  in  the  race  is 
by  natural  selection  of  congenital  variations.  The  theory  of  natural 
selection  may  be  stated  briefly  as  follows :  Organisms  vary  in  many 
ways,  through  variations  affecting  the  germ  cells.  Among  these  varia- 
tions are  some  that  help  the  organism,  making  it  more  efficient  in  escap- 
ing enemies  or  in  obtaining  food.  These  organisms,  therefore,  survive, 
while  those  without  these  helpful  variations  are  killed.  The  surviving 
organisms  transmit  their  helpful  congenital  variations  to  their  offspring, 


DEVELOPMENT  OF  BEHAVIOR  321 

so  that  in  time  an  entire  race  may  show  the  characteristics  which  first 
arose  as  accidental  variations  along  with  many  other  useless  ones. 

A  great  objection  to  this  theory  has  been  that  it  deals  merely  with 
chance  variations  in  all  directions,  so  that  progress  along  a  definite  line, 
it  is  said,  could  never  be  brought  about  through  it.  The  race  progresses 
just  as  the  individuals  do;  what  is  first  acquired  by  the  individual  is 
later  acquired  by  the  race,  as  if  the  law  of  progress  were  the  same  in  the 
two  cases.  This,  it  is  held,  could  not  be  brought  about  through  the 
selection  of  chance  variations  in  all  directions. 

In  recent  years  a  most  successful  attempt  has  been  made  by  J.  Mark 
Baldwin  (1902)  and  others  to  show  that  this  objection  is  not  a  valid  one; 
that  the  action  of  natural  selection  on  characters  playing  a  part  in  the 
behavior  would,  in  fact,  be  guided  by  laws  similar  to  or  identical  with 
those  controlling  the  progress  of  the  individual.  To  this  guidance  the 
name  organic  selection  has  been  given.  Organic  selection  would  then 
account  for  the  progress  of  the  race  in  a  continuous  manner  and  in  a 
definite  direction.  We  shall  examine  briefly,  from  this  point  of  view, 
the  action  of  natural  selection  on  behavior  in  the  lower  organisms. 

Observation  and  experiment  show  that  there  exist  such  variations 
in  the  behavior  of  lower  organisms  as  would  under  certain  circumstances 
give  opportunity  for  the  action  of  natural  selection.  If  into  an  area 
containing  Paramecia  a  drop  of  a  10  per  cent  sugar  solution  is  introduced, 
most  of  the  animals  enter  it  and  are  killed,  but  a  few  react  negatively 
on  coming  in  contact  with  it,  and  escape.  If  such  solutions  were  a  con- 
stant feature  of  the  environment,  it  seems  probable  that  in  time  there 
would  be  produced  through  selection  a  race  of  Paramecia  that  would 
always  react  negatively  to  them,  and  would,  therefore,  not  be  endan- 
gered by  their  existence.  Similar  differences  exist  among  different  indi- 
viduals as  to  sensitiveness  to  other  chemicals,  to  heat,  and  to  electricity, 
as  we  have  seen  in  previous  pages.  There  is  thus  undoubtedly  an  oppor- 
tunity for  the  action  of  natural  selection  to  produce  a  race  of  organisms 
more  sensitive  to  weak  stimuli  than  is  the  average  at  present,  if  the  en- 
vironment should  require  it.  But  if  the  environment  does  not  require  it, 
the  action  of  natural  selection,  like  that  of  individual  accommodation, 
will  not  bring  it  about.  By  either  method  only  that  is  preserved  which 
is  useful. 

There  is  likewise  clearly  an  opportunity  for  natural  selection  to  pro- 
duce a  race  showing  increased  precision  and  adaptiveness  in  the  move- 
ments brought  about  by  stimulation.  As  we  have  seen  on  page  305,  the 
reactions  of  Paramecium  to  heat  are  so  much  more  effective  than  those 
of  Bursaria  that  if  locally  heated  regions  were  part  of  the  usual  environ- 
ment of  the  two  organisms,  the  Bursaria?  would,  for  the  greater  part, 


322  BEHAVIOR   OF    THE   LOWER   ORGANISMS 

soon  be  killed,  while  the  Paramecia  would  not  suffer.  The  latter  would, 
therefore,  be  selected,  as  compared  with  the  former.  But  there- exist 
variations  of  reaction  even  among  individuals  of  the  same  species. 
Some  specimens  of  Bursaria  when  stimulated  by  heat  show  a  greater 
inclination  to  swim  freely,  revolving  on  the  long  axis,  than  do  the  ma- 
jority, that  sink  quickly  to  the  bottom  and  cease  to  revolve.  The  former 
are  saved  from  the  heat,  while  the  latter  are  killed.  In  time  there  might 
thus  be  developed  a  race  of  Bursarias  that  were  as  well  protected  by  their 
behavior  from  the  action  of  heat  as  are  Paramecia. 

What  are  the  characteristics  that  would  be  preserved  by  natural 
selection?  First  it  seems  clear  that  under  usual  conditions  the  regula- 
tive power  would  tend  to  be  preserved.  So  long  as  the  environment  is 
a  changing  one,  those  individuals  that  can  alter  their  behavior  to  lit  the 
new  conditions  would  live,  while  any  that  cannot  do  so  will  be  killed, 
so  that  any  variation  in  the  direction  of  less  regulative  power  will  be  cut 
off.  But  under  quite  uniform  conditions  there  might  be  no  advantage 
in  this  regulative  power,  and  no  selection  based  upon  it. 

Second,  those  variations  will  be  preserved  that  are  in  line  with  the 
general  tendency  of  the  behavior.  In  other  words,  those  variations  will 
persist  that  tend  in  the  same  direction  as  the  adaptation  of  the  individuals, 
due  to  selection  of  overproduced  movements  and  the  law  of  the  resolu- 
tion of  physiological  states.     This  will  be  made  clear  by  an  illustration. 

Most  ciliate  infusoria  may  swim  freely  through  the  water,  may  creep 
along  surfaces,  may  exude  mucus  to  form  a  cyst,  and  may  burrow  about 
in  the  debris  at  the  bottom  of  the  water.  Some  show  one  habit  in  a  more 
marked  way,  others  another.  Let  us  suppose  a  ciliate  infusorian  with  a 
cylindrical  body  covered  uniformly  with  cilia,  that  may  behave  in  all 
these  ways.  It  responds  to  stimulation  by  trial  of  the  different  reactions 
which  it  has  at  command,  continuing,  in  accordance  with  the  principle 
of  the  resolution  of  physiological  states,  that  reaction  which  proves 
successful.  Suppose  that  a  number  of  the  individuals  come  thus  to 
react  habitually  in  the  first  of  the  four  ways  mentioned  above,  others  in 
the  second,  others  in  the  third,  and  still  others  in  the  fourth.  All  these 
different  methods  have  advantages  for  meeting  unfavorable  conditions, 
and  all  are  found  as  a  prevailing  reaction  in  different  ciliates. 

We  have  then  four  groups  of  ciliate  organisms,  all  alike  structurally, 
but  with  different  habits.     How  will  natural  selection  act  on  these? 

(i)  In  the  first  group,  that  swim  freely  through  the  water,  like  Para- 
mecium, all  variations  that  favor  quickness  of  reaction,  rapidity  of  move- 
ment, and  precision  of  direction  will  be  advantageous,  and  the  indi- 
viduals possessing  them  will  tend  to  be  selected.  Specimens  with  body 
ill-shaped  for  rapid  movement,  with  cilia  weak  or  unequally  distributed, 


DEVELOPMENT  OF  BEHAVIOR  323 

or  with  awkward  methods  of  moving,  will  be  killed  by  their  inability 
to  escape  with  sufficient  rapidity  from  powerful  agents.  There  will 
thus  .be  a  tendency  to  develop  a  fishlike  form,  adapted  for  rapid  move- 
ments through  the  water;  close-set,  uniform  cilia,  and  a  tendency  to 
revolve  on  the  long  axis ;  in  other  words,  such  characteristics  as  we  find 
in  Paramecium. 

(2)  In  the  second  group,  which  reacts,  like  Oxytricha,  by  running 
along  the  bottom,  variations  of  an  entirely  different  character  will  be 
advantageous.  The  original  cylindrical  form  can  bring  but  few  of  its 
cilia  against  a  surface,  and  presents  much  resistance  to  the  water.  Varia- 
tions in  the  direction  of  a  flat  form,  bringing  many  cilia  against  the 
surface,  and  presenting  little  resistance  to  the  water  as  it  runs  along, 
will  be  advantageous,  and  individuals  with  such  variations  will  be  se- 
lected. The  cilia  on  the  surface  kept  against  the  bottom  will  be  the  all- 
important  ones,  so  variations  in  the  direction  of  increased  size,  strength, 
and  rapidity  of  these  cilia  will  be  preserved ;  they  will  develop  into 
"cirri"  and  other  leglike  structures.  The  cilia  on  the  upper  side  of 
the  body  will  be  not  merely  useless,  but  a  hindrance;  hence  they  will 
tend  to  be  lost.  The  tendency  to  revolve  on  the  long  axis  will  be  in- 
jurious and  will  likewise  tend  to  disappear  by  selection  of  those  that 
do  not  thus  revolve.  In  this  way,  under  the  action  of  natural  selection, 
an  organism  will  be  developed  having  totally  different  characteristics 
from  the  organisms  of  the  first  set,  that  react  by  swimming  freely.  It 
will  naturally  approach  the  characteristics  shown  by  Stylonychia,  rather 
than  those  of  Paramecium. 

(3)  On  the  third  organism,  which  reacts  to  intense  agents  by  secret- 
ing a  layer  of  mucus  about  itself,  natural  selection  will  act  in  a  still 
different  manner.  There  will  be  no  tendency  to  select  rapidly  moving 
individuals,  nor  those  having  larger  or  more  numerous  cilia,  nor  those 
having  cilia  distributed  in  any  special  way;  all  these  characteristics 
will  indeed  be  disadvantageous.  Spiral  swimming  will  not  be  developed. 
Those  organisms  that  produce  a  thicker  layer  of  mucus,  of  a  more  re- 
sistant character,  and  do  this  the  more  rapidly,  will  be  selected. 

(4)  The  fourth  organism,  which  habitually  reacts  by  burrowing 
into  the  detritus  at  the  bottom  of  the  water,  will  be  acted  upon  by  natu- 
ral selection  in  a  still  different  way.  Only  those  characteristics  which 
aid  the  burrowing  will  be  useful  and  therefore  selected.  There  will 
be  no  tendency  to  produce  a  swiftly  swimming  organism,  nor  one  adapted 
to  running  along  the  bottom,  nor  one  secreting  a  thick  and  resistant 
layer  of  mucus. 

To  sum  up,  it  appears  that  only  those  variations  are  of  advantage 
that  are  used,  and  only  such  variations  can  be  preserved  by  the  action 


324 


BEHAVIOR   OF   THE  LOWER   ORGANISMS 


of  natural  selection.  Only  such  characteristics  can  be  selected  as  are 
in  line  with  the  efforts  of  the  organism.  A  variation  which  might  be  of 
inestimable  advantage  to  an  organism  that  reacts  by  swimming  would 
be  entirely  lost  on  one  that  burrows  in  the  earth.  The  organism  deter- 
mines by  its  own  actions  the  direction  of  its  development  under  the 
action  of  natural  selection.  When  it  adopts  a  certain  line  of  behavior, 
it  decides  to  a  large  degree  the  future  career  of  the  race.  Development 
through  the  action  of  natural  selection  must  then  follow  as  definite  a 
trend  as  does  the  behavior  of  the  individual  and  indeed  the  same  trend, 
for  it  is  guided  by  this  behavior.  Individual  selection  guides  natural 
selection. 

Individual  selection,  with  its  production  of  definite  adaptive  reac- 
tions, is  due,  of  course,  to  selection  from  varied  movements,  later  fixed 
by  the  law  of  the  readier  resolution  of  physiological  states.1  With  this 
in  mind,  we  may  express  what  we  have  just  brought  out  as  follows :  In- 
dividual selection  (intelligence)  and  natural  selection  are  merely  different 
methods  of  selecting  adaptive  ways  of  reacting.  The  former  selects 
the  adaptive  response  from  among  diverse  reactions  of  the  same  indi- 
vidual; while  natural  selection  selects  the  adaptive  response  from  among 
diverse  reactions  of  different  individuals. 

This  may  be  illustrated  as  follows:  Let  us  suppose  an  organism 
whose  action  system  includes  the  different  acts  i,  2,  3,  4,  5,  6,  7,  8,  9. 
When  the  physiological  processes  of  this  animal  are  interfered  with  by 
external  agents,  it  tends  to  run  through  these  nine  reactions,  in  the  order 
given  above  —  as  Stentor  runs  through  its  four  or  five  reactions.  Sup- 
pose that  under  a  certain  frequently  recurring  injurious  condition  the 
reaction  7  is  the  adaptive  one,  relieving  the  interference  with  the  physio- 
logical processes.  The  organism  runs  through  the  series  to  7,  then  stops 
(since  the  cause  for  further  reaction  has  ceased).  It  now  retains  this 
reaction  as  the  immediate  response  to  the  given  condition,  through  the 
law  of  the  readier  resolution  of  physiological  states.  Many  of  the  indi- 
viduals are  killed  before  7  is  reached,  but  after  this  adaptive  reaction  has 
become  fixed,  no  others  are  killed.  The  young  of  these  individuals 
must,  however,  begin  at  the  beginning  of  the  series,  so  that  many  will 
be  destroyed. 

Let  us  suppose  that  in  another  group  there  are,  among  many  different 
individuals,  congenital  variations  in  the  order  in  which  the  nine  re- 
sponses are  given.  Some  respond  by  the  series  2,  3,  7,  1,  4,  5,  6,  8,  9. 
These  reach  the  adaptive  reaction  7  sooner  than  do  those  following  the 
usual  order,  hence  fewer  are  killed  by  the  injurious  condition.  Others 
react  in  the  order  7,  4,  3,  5,  1,  2,  6,  8,  9.     The  first  reaction  is  here  the 

1  This  is  the  process  known  as  intelligence,  in  higher  animals.     See  Chapter  XX. 


DEVELOPMENT  OF  BEHAVIOR  325 

adaptive  one.  Hence  the  series  goes  no  farther  (since  the  cause  for 
reaction  ceases  at  once),  and  these  organisms  are  not  killed  at  all  by  the 
injurious  condition.  They  are  thus  selected,  as  compared  with  those 
reacting  in  the  usual  way,  and  their  method  of  reacting,  being  congenital, 
is  inherited  by  posterity.  In  the  course  of  time  all  the  remaining  indi- 
viduals of  this  group  will  respond  at  once,  like  those  of  the  previous 
group,  by  the  reaction  7. 

Thus  individual  selection  and  natural  selection  necessarily  work  to 
the  same  result.  One  selects  from  among  the  different  acts  of  the  same 
individual,  the  other  from  among  those  of  different  individuals.  The  thing 
selected  is  the  same  in  each  case,  —  namely,  the  adaptive  reaction. 

If  there  exist  at  the  same  time  the  power  of  individual  modification 
and  the  variations  on  which  natural  selection  acts,  then  under  uniform 
conditions  the  latter  will  be  more  effective,  since  it  results  in  immediate 
response  by  the  adaptive  reaction,  while  the  former  requires  that  every 
new  individual  should  go  through  the  trial  series,  with  its  attendant 
dangers  of  destruction.  If  the  conditions  are  very  severe,  in  time  only 
the  individuals  which  have  inherited  the  immediate  adaptive  response 
will  survive.  Thus,  through  the  action  of  natural  selection  these  or- 
ganisms will  have  an  inborn  tendency  to  react  directly  in  an  adaptive 
way,  whereas  in  previous  generations  most  of  the  individuals  of  the  race 
acted  in  this  manner  only  as  a  result  of  individual  modification  through 
experience. 

Furthermore,  it  may  be  pointed  out  that  in  the  course  of  time  an 
organism  which  had  adopted  some  special  type  of  behavior,  as  burrow- 
ing, would  become  quite  unadapted  to  other  behavior,  as  running  along 
the  bottom  or  swimming  through  the  water.  It  develops  structures, 
under  the  influence  of  its  adaptive  behavior,  that  make  it  difficult  or 
perhaps  impossible  for  the  organism  to  react  in  any  other  way  than  by 
burrowing.  After  a  time,  then,  it  will  lose  all  tendency  to  react  in  other 
ways,  because  it  cannot  react  in  other  ways,  owing  to  the  structural 
changes  it  has  undergone.  In  most  cases  the  specialization  will  not  go 
so  far  as  this,  and  the  organism  will  retain  the  power  of  attempting  other 
methods  of  reaction;  that  is,  of  performing  other  movements.  But 
these  movements  will  be  ineffectual,  because  the  structures  of  the  or- 
ganism are  not  adapted  to  their  performance.  They  will  therefore 
not  relieve  the  organism  from  stimuli ;  hence  they  will  be  quickly 
exchanged  for  the  movements  which  are  effective.  Thereafter  the  or- 
ganism will  always  react  by  these  movements  on  which  its  structure  is 
based.  If  these  first  few  ineffectual  movements  are  not  observed,  it 
will  appear  that  the  organism  has  been  rigidly  limited  from  the  beginning 
to  this  one  type  of  behavior.     Apparently  there  exist  few  if  any  organisms 


326  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

which  do  not  show,  in  their  younger  stages  at  least,  a  few  such  ineffectual 
movements. 

Baldwin  suggests  that  the  same  process  may  go  farther  than  this, 
in  the  following  way:  After  the  development,  under  the  influence  of 
a  certain  reaction  method,  of  structures  fitted  to  carry  out  that  method, 
another  congenital  variation  may  occur,  by  which  energy  will  be  dis- 
charged directly  into  this  apparatus,  in  the  way  necessary  for  perform- 
ing the  accustomed  reaction,  without  any  previous  trial.  It  is  urged  that 
after  the  apparatus  has  been  developed,  the  further  variation  required 
would  probably  be  slight  and  not  unlikely  to  occur.  The  organisms 
having  this  variation  must  react  more  readily  and  rapidly  than  those  in 
which  a  trial  is  required,  hence  they  might  be  selected.  Thus  in  time 
in  the  entire  race  the  reaction  would  be  limited  to  this  particular  method. 
There  seems  to  be  no  theoretical  difficulty  as  to  the  occurrence  of  such 
a  variation ;  if  it  occurs,  development  would  doubtless  take  place  in  the 
way  set  forth,  provided  the  environment  remain  sufficiently  constant. 
But  perhaps  there  would  be  little  difference  in  reality  between  the  be- 
havior of  such  an  organism,  and  one  which  had  merely  developed  such 
structures  as  to  make  difficult  any  kind  of  reaction  save  one.  The  latter 
would  still  reserve  the  capability  of  developing  other  reactions,  under 
changed  circumstances,  while  the  former  would  not. 

The  guidance  of  natural  selection  by  the  actions  of  the  individuals 
that  we  have  illustrated  above,  is  what  has  been  called  "organic  selec- 
tion." The  latter  is  evidently  merely  an  exposition  of  how  natural 
selection  acts,  not  anything  additional  to  natural  selection,  or  differing 
from  it  in  principle.  For  a  general  discussion  of  the  questions  which 
it  involves,  reference  should  be  made  to  J.  Mark  Baldwin's  "Develop- 
ment and  Evolution." 

Is  natural  selection,  thus  guided  by  individual  accommodation,  suf- 
ficient to  account  for  the  progress  of  the  race  in  behavior?  It  is  clear 
that  natural  selection  cannot  account  for  the  origin  of  anything;  only 
that  can  be  selected  which  already  exists.  All  the  potency  of  behavior 
and  of  everything  else  that  exists  must  lie  in  the  laws  of  matter  and 
energy,  —  physical  and  chemical,  and  possibly  vital  laws.  Whatever 
the  part  assigned  to  natural  selection,  the  superlative  importance  of 
these  laws  remains ;  they  must  continue  the  chief  field  for  scientific  inves- 
tigation. All  that  natural  selection  is  called  upon  to  explain  is  the  fact 
that  at  a  given  time  such  and  such  particular  manifestations  of  these 
general  laws  exist,  rather  than  certain  other  manifestations.  In  the  field 
of  behavior  it  is  called  to  explain  only  the  fact  that  this  particular  organ- 
ism now  behaves  in  this  particular  way,  rather  than  in  some  other  one 
of  the  infinite  number  of  possible  ways.     Can  it  explain  this? 


DEVELOPMENT   OF   BEHAVIOR  ?>21 

The  fact  is  established  that  organisms  which  vary  in  such  a  way  as 
to  make  them  unfitted  to  carry  out  the  functions  which  they  undertake 
are  destroyed.  The  correlative  fact  that  organisms  which  vary  in  such 
a  way  as  to  perform  their  functions  better  than  the  average  are  not  so 
usually  destroyed,  is  likewise  established.  The  further  fact  is  established 
that  such  congenital  variations  occur  and  are  often  handed  on  to  the  off- 
spring. These  three  facts  show  that  natural  selection  is  beyond  ques- 
tion a  factor  in  the  development  of  behavior.  The  only  question  is  as 
to  the  extent  of  its  agency.  This  depends  on  the  number  and  extent 
of  the  congenital  variations  that  occur.  If  these  are  sufficiently  numer- 
ous and  sufficiently  varied,  then  it  seems  clear  that  natural  selection 
guided  by  individual  accommodation,  would  produce  the  results  which  we 
see.  Its  method  of  action  is  exactly  what  is  needed  to  produce  the  ob- 
served results;  the  only  question  is  whether  the  material  presented  to 
it  in  congenital  variations  is  sufficient.  The  answer  to  this  question 
must  come,  if  it  ever  comes,  from  that  study  of  variations  which  has 
received  such  an  impulse  in  recent  years.  The  recent  studies  of  De 
Vries  in  mutation  seem  especially  promising  from  this  point  of  view.  If 
it  should  appear  that  the  material  presented  by  congenital  variations  is 
not  sufficient  to  account  for  the  observed  development,  we  should  be 
forced  apparently  to  turn  once  more  to  the  possibility  of  the  inheritance 
of  the  characteristics  developed  during  the  lifetime  of  the  organism. 
The  question  of  the  inheritance  of  acquired  characters  cannot  as  yet  be 
considered  finally  settled. 

The  view  that  the  development  of  behavior  is  based  largely  on  selec- 
tion from  among  varied  movements,  with  subsequent  retention  of  the 
selected  movements,  to  which  we  have  come  through  a  study  of  the  be- 
havior of  the  lower  organisms,  is  of  course  not  a  new  one.  A  theory 
to  this  effect  has  been  set  forth  by  Spencer  and  Bain,  and  has  been 
especially  developed  in  recent  years  by  J.  Mark  Baldwin.  The  obser- 
vations set  forth  in  the  present  work  lead  to  views  differing  in  some 
important  respects  from  these  developed  by  Baldwin  and  Bain,  par- 
ticularly as  to  the  nature  of  the  causes  which  produce  the  varied  move- 
ments. Space  will  not  permit  our  entering  here  into  a  discussion  of 
these  differences.  The  reader  may  be  referred  for  a  discussion  of  some 
of  the  general  bearings  of  this  theory  to  the  two  volumes  of  Baldwin 
(1897,  1902).  Possibly  the  most  lucid  statement  of  this  theory,  in  its 
general  bearings,  is  that  recently  given  by  Hobhouse  (1901). 

LITERATURE   XIX 

Baldwin.  1897,  1902;  Hobhouse,  1901  :  Spencer,  1894  (Section  236.  pp.  244' 
245)  ;  Bain,  1888  (p.  315)  :   1894  (pp.  323.  324). 


CHAPTER  XX 

RELATION     OF    BEHAVIOR    IN    LOWER    ORGANISMS    TO    PSYCHIC 

BEHAVIOR 

In  describing  the  behavior  of  lower  organisms  we  have  used  in  the 
present  work,  so  far  as  possible,  objective  terms  —  those  having  no  im- 
plication of  psychic  or  subjective  qualities.  We  have  looked  at  organ- 
isms as  masses  of  matter,  and  have  attempted  to  determine  the  laws  of 
their  movements.  In  ourselves  we  find  movements  and  reactions  re- 
sembling in  some  respects  those  of  the  lower  organisms.  We  draw  away 
from  heat  and  cold  and  injurious  chemicals,  just  as  Paramecium  does. 
Our  behavior  depends  on  physiological  states,  as  does  that  of  Stentor. 
But  in  ourselves  there  is  the  very  interesting  additional  fact  that  these 
movements,  reactions,  and  physiological  states  are  often  accompanied  by 
subjective  states,  —  states  of  consciousness.  Different  states  of  con- 
sciousness are  as  varied  as  the  different  possibilities  of  reaction ;  indeed, 
more  varied.  In  speaking  of  behavior  in  ourselves,  and  as  a  rule  in 
higher  animals,  we  use  terms  based  on  these  subjective  states,  as  pleas- 
ure and  pain,  sensation,  memory,  fear,  anger,  reason,  and  the  like. 

The  peculiarity  of  subjective  states  is  that  they  can  be  perceived 
only  by  the  one  person  directly  experiencing  them,  —  by  the  subject. 
Each  of  us  knows  directly  states  of  consciousness  only  in  himself.  We 
cannot  by  observation  and  experiment  detect  such  states  in  organisms 
outside  of  ourselves.  But  observation  and  experiment  are  the  only 
direct  means  of  studying  behavior  in  the  lower  organisms.  We  can 
reason  concerning  their  behavior,  and  through  reasoning  by  analogy 
we  may  perhaps  conclude  that  they  also  have  conscious  states.  But 
reasoning  by  analogy,  when  it  is  afterward  tested  by  observation  and 
experiment,  has  often  shown  itself  fallacious,  so  that  where  it  cannot 
be  tested,  we  must  distrust  its  conclusiveness.  Moreover,  in  different 
men  it  leads  to  different  conclusions,  so  that  it  does  not  result  in  ad- 
mitted certainty.  Hence  it  seems  important  to  keep  the  results  of  obser- 
vation and  experiment  distinct  from  those  of  reasoning  by  analogy,  so 
that  we  may  know  what  is  really  established.  On  this  account  it  is 
customary  among  most  physiologists  not  to  use,  in  discussing  the  be- 
havior of  the  lower  organisms,  psychic  terms,  or  those  implying  sub- 

328 


RELATION   TO  PSYCHIC  BEHAVIOR  329 

jective  states.  This  has  the  additional  ground  that  the  ideal  of  most 
scientific  men  is  to  explain  behavior  in  terms  of  matter  and  energy,  so 
that  the  introduction  of  psychic  implications  is  considered  superfluous. 

While  this  exclusive  use  of  objective  terms  has  great  advantages,  it 
has  one  possible  disadvantage.  It  seems  to  make  an  absolute  gulf  be- 
tween the  behavior  of  the  lower  organisms  on  the  one  hand,  and  that  of 
man  and  higher  animals  on  the  other.  From  a  discussion  of  the  be- 
havior of  the  lower  organisms  in  objective  terms,  compared  with  a  dis- 
cussion of  the  behavior  of  man  in  subjective  terms,  we  get  the  impression 
of  complete  discontinuity  between  the  two. 

Does  such  a  gulf  actually  exist,  or  does  it  lie  only  in  our  manner  of 
speech?  We  can  best  get  evidence  on  this  question  by  comparing  the 
objective  features  of  behavior  in  lower  and  in  higher  organisms.  In 
any  animal  outside  of  man,  and  even  in  man  outside  of  the  self,  the 
existence  of  perception,  choice,  desire,  memory,  emotion,  intelligence, 
reasoning,  etc.,  is  judged  from  certain  objective  facts  —  certain  things 
which  the  organisms  do.  Do  we  find  in  the  lower  organisms  objective 
phenomena  of  a  similar  character,  so  that  the  same  psychic  names  would 
be  applied  to  them  if  found  in  higher  organisms?  Do  the  objective 
factors  in  the  behavior  of  lower  organisms  follow  laws  that  are  similar 
to  the  laws  of  psychic  states  ?  Only  by  comparing  the  objective  factors 
can  we  determine  whether  there  is  continuity  or  a  gulf  between  the  be- 
havior of  lower  and  higher  organisms  (including  man),  for  it  is  only 
these  factors  that  we  know. 

Let  us  then  examine  some  of  the  concepts  employed  in  discussions 
of  the  behavior  of  higher  animals  and  man,  determining  whether  there 
exist  any  corresponding  phenomena  in  lower  organisms.  We  shall  not 
attempt  to  take  into  consideration  the  scholastic  definitions  of  the  terms 
used,  but  shall  judge  of  them  merely  from  the  objective  phenomena  on 
which  they  are  based. 

When  we  say  that  an  animal  perceives  something,  or  that  it  shows 
perception  of  something,  we  base  this  statement  on  the  observation  that 
it  reacts  in  some  way  to  this  thing.  On  the  same  basis  we  could  make 
the  statement  that  Amoeba  perceives  all  classes  of  stimuli  which  we  our- 
selves perceive,  save  sound  (which  is,  however,  essentially  one  form  of 
mechanical  stimulation).  Perception  as  judged  from  our  subjective 
experiences  means  much  more:  how  much  of  this  may  be  present  in 
animals  outside  the  self  we  cannot  know. 

Discrimination  is  a  term  based,  so  far  as  objective  evidence  goes, 
upon  the  observed  fact  that  organisms  react  differently  to  different 
stimuli.  In  this  sense  Paramecium,  as  we  have  seen,  discriminates 
acids  from  alkalies ;  Amoeba  discriminates  a  Euglena  cyst  from  a  grain 


330  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

of  sand,  and  in  general  all  lower  organisms  show  discrimination  in  many 
phases  of  their  behavior. 

Choice  is  a  term  based  objectively  on  the  fact  that  the  organism  ac- 
cepts or  reacts  positively  to  some  things,  while  it  rejects  or  reacts  nega- 
tively or  not  at  all  to  others.  In  this  sense  all  lower  organisms  show 
choice,  and  at  this  we  need  not  be  surprised,  for  inorganic  substances 
show  a  similar  selectiveness.  The  distinctive  thing  about  the  choice  of 
organisms  is  that  it  is  regulatory ;  organisms  on  the  whole  choose  those 
things  which  aid  their  normal  life  processes  and  reject  those  that  do  not. 
This  is  what  justifies  the  use  of  the  term  "choice,"  as  contrasted  with 
the  mere  selectiveness  of  inorganic  reactions.  Choice  in  this  regulatory 
sense  is  shown  by  lower  organisms,  as  we  have  seen  in  detail  in  previous 
chapters.  Choice  is  not  perfect,  from  this  point  of  view,  in  either  lower 
or  higher  organisms.  Paramecium  at  times  accepts  things  that  are  use- 
less or  harmful  to  it,  but  perhaps  on  the  whole  less  often  than  does  man. 

The  methods  by  which  choice  is  shown  in  particular  organisms  have 
been  set  forth  in  our  descriptive  chapters.  We  may  refer  particularly 
to  the  account  of  choice  in  the  infusoria,  given  on  page  183.  The  free- 
swimming  infusoria  as  they  move  about  are  continually  rejecting  cer- 
tain things  and  accepting  others,  and  this  choice  is  regulatory.  Their 
behavior  is  based  throughout  on  the  method  of  trial,  and  this 
involves  an  act  comparable  to  choice  in  almost  every  detail.  Whatever 
the  condition  met,  the  infusorian  must  either  accept  it  by  going  ahead, 
or  reject  it  by  backing  and  giving  the  avoiding  reaction.  We  can  al- 
most say  that  its  whole  behavior  is  a  process  of  choice;  that  choice  is 
the  essential  feature  of  its  behavior.  For  the  other  lower  organisms 
that  we  have  taken  up,  a  consideration  of  details  would  discover 
activities  involving  regulatory  choice  almost  as  continuously  as  in  the 
infusoria. 

Is  not  what  we  call  attention  in  higher  organisms,  when  considered 
objectively,  the  same  phenomenon  that  we  have  called  the  interference 
of  one  stimulus  with  the  reaction  to  another?  At  the  basis  of  attention 
lies  objectively  the  phenomenon  that  the  organism  may  react  to  only  one 
stimulus  even  though  other  stimuli  are  present  which  would,  if  acting 
alone,  likewise  produce  a  response.  The  organism  is  then  said  to  at- 
tend to  the  particular  stimulus  to  which  it  responds.  This  fundamental 
phenomenon  is  clearly  present  in  unicellular  organisms.  Stentor  and 
Paramecium  when  reacting  to  contact  with  a  solid  "pay  no  attention" 
to  a  degree  of  heat  or  a  chemical  or  an  electric  current  that  would  pro- 
duce an  immediate  reaction  in  a  free  individual.  On  the  other  hand, 
individuals  reacting  to  heat  or  a  chemical  may  not  respond  to  contact 
with  a  mass  of  bacteria,  to  which  they  would  under  other  conditions 


RELATION   TO   PSYCHIC  BEHAVIOR  331 

react  positively.     In  our  chapter  on  reaction  under  two  or  more  stimuli 
in  the  infusoria,  many  examples  of  this  character  are  given. 

Indeed,  attention  in  this  objective  sense  seems  a  logical  necessity  for 
the  behavior  of  any  organism  having  at  its  command  more  than  a  single 
action.  The  characteristic  responses  to  two  present  stimuli  may  be  in- 
compatible with  each  other.  The  organism  must  then  react  to  one  or 
the  other,  since  it  cannot  react  to  both;  it  thus  attends  (objectively)  to 
one,  and  not  to  the  other.  Only  in  case  there  is  no  reaction  at  all  in 
the  presence  of  two  stimuli,  or  in  case  its  reaction  is  precisely  inter- 
mediate between  those  required  by  the  two,  could  the  basis  of  attention 
be  considered  lacking.  i\n  organism  behaving  in  this  way  would  be 
quickly  destroyed  as  a  result  of  its  indecisive  and  ineffective  behavior. 

In  higher  animals  and  man  we  distinguish  certain  different  condi- 
tions,—  "states  of  feeling,"  "emotions,"  "appetites,"  "desires,"  and 
the  like.  In  all  cases  except  the  self,  these  various  states  are  distin- 
guished through  the  fact  that  the  organism  behaves  differently  in  the 
different  conditions,  even  though  the  external  stimuli  may  be  the  same. 
We  find  a  parallel  condition  of  affairs  in  the  lower  organisms.  Here, 
as  we  have  seen,  the  behavior  under  given  external  conditions  depends 
largely  on  the  physiological  condition  of  the  individual.  Many  illus- 
trations of  this  fact  are  given  in  preceding  chapters,  so  that  we  need  not 
dwell  upon  it  here. 

In  the  lower  organisms  we  can  even  distinguish  a  number  of  states 
that  are  parallel,  so  far  as  observation  can  show,  with  those  distin- 
guished and  named  in  higher  animals  and  man.  To  begin  with  some 
of  the  simpler  ones,  the  objective  correlate  of  hunger  can  be  distin- 
guished at  least  as  low  in  the  scale  as  Hydra  and  the  sea  anemone. 
These  animals,  as  we  have  seen,  take  food  only  when  hungry,  and  if 
very  hungry,  will  take  substances  as  food  which  they  otherwise  reject. 
Doubtless  hunger  could  be  detected  in  still  lower  organisms  by  proper 
experiments.  A  resting  condition  comparable  to  sleep  is  found,  as  we 
have  seen,  in  the  flatworm  (p.  253),  while  there  seems  to  be  no  indica- 
tion of  such  a  state  in  the  infusoria  (p.  181).  Fatigue  can  of  course  be 
distinguished  in  all  living  things,  including  separated  muscles. 

Correlative  with  hunger,  there  exists  a  state  which  corresponds  so 
far  as  objective  evidence  goes  with  what  we  should  call  in  higher  animals 
a  desire  for  food.  Hydra  when  hungry  opens  its  mouth  widely  when 
immersed  in  a  nutritive  liquid.  In  the  flatworm,  we  can  distinguish 
a  certain  physiological  condition  in  which  the  animal  moves  about  in 
an  eager,  searching  way,  as  if  hunting  for  food.  Even  in  Amoeba  we 
find  a  pertinacity  in  the  pursuit  of  food  (p.  14  and  Fig.  21)  such  as  we 
would  attribute  in  a  higher  animal  to  a  desire  for  it. 


332  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

All  the  way  up  the  scale,  from  Amoeba  and  bacteria  to  man,  we  find 
that  organisms  react  negatively  to  powerful  and  injurious  agents.  In 
man  and  higher  animals  such  reactions  are  usually  said  to  be  due  to 
pain.  In  the  lower  organisms  the  objective  facts  are  parallel,  and  natu- 
rally lead  to  the  assumption  of  a  physiological  state  similar  to  what  we 
have  in  the  higher  forms.  As  to  subjective  accompaniments  of  such 
a  state  we  of  course  know  nothing  in  animals  other  than  ourselves.  The 
essential  cause  of  the  states  corresponding  to  pain  is  "interference  with 
any  of  the  processes  of  which  the  organism  is  the  seat,  and  the  correlate 
in  action  of  these  states  is  a  change  in  movement.  This  point  will 
be  developed  in  our  final  chapter. 

A  similar  basis  exists  for  distinguishing  throughout  the  organic 
series  a  physiological  state  corresponding  to  that  accompanying  pleasure 
in  man.  This  is  correlated  with  a  relief  from  interference  with  the  life 
processes,  or  with  the  uninterrupted  progression  of  these  processes. 

In  man  and  higher  animals  we  often  find  a  negative  reaction  to  that 
which  is  not  in  itself  injurious,  but  which  is  usually  followed  by  some- 
thing injurious.  The  sight  of  a  wild  beast  is  not  injurious,  considered 
by  itself,  but  as  preceding  actual  and  injurious  contact  with  this  beast, 
it  leads  to  powerful  negative  reactions.  Such  reactions  are  said  to  be 
due  to  jear.  In  fear  there  is  then  a  negative  reaction  to  a  representative 
stimulus  —  one  that  stands  for  a  really  injurious  stimulation.  In  lower 
organisms  we  find  the  objective  indications  of  a  parallel  state  of  affairs. 
The  infusoria  react  negatively  to  solutions  of  chemicals  that  are  not, 
so  far  as  we  can  determine,  injurious,  though  they  would  naturally, 
under  ordinary  circumstances,  be  immediately  followed  by  a  solution 
so  strong  as  to  be  injurious.  Euglena  reacts  negatively  when  darkness 
affects  only  its  colorless  anterior  end,  though  we  have  reason  to  believe 
that  it  is  only  the  green  part  of  the  body  which  requires  the  light  for  the 
proper  discharge  of  its  functions.  A  much  clearer  case  is  seen  in  the 
sea  urchin,  which  reacts  by  defensive  movements  when  a  shadow  falls 
upon  it,  though  shade  is  favorable  to  its  normal  functions.  Objectively, 
fear  has  at  its  basis  the  fact  that  a  negative  reaction  may  be  produced 
by  a  stimulus  which  is  not  in  itself  injurious,  provided  it  leads  to  an 
injurious  stimulation  ;  this  basis  we  find  throughout  organisms. 

Sometimes  higher  animals  and  man  are  thrown  into  a  "state  of 
fear,"  such  that  they  react  negatively  to  all  sorts  of  stimuli,  that  under 
ordinary  circumstances  would  not  cause  such  a  reaction.  A  similar 
condition  of  affairs  we  have  seen  in  Stentor  and  the  flatworm.  After 
repeated  stimulation,  they  react  negatively  to  all  stimuli  to  which  they 
react  at  all. 

The  general  fact  of  which  the  reactions  through  fear  are  only  a  special 


RELATION   TO   PSYCHIC    BEHAVIOR  333 

example  is  the  following:  Organisms  react  appropriately  to  repre- 
sentative stimuli.  That  is,  they  react,  not  merely  to  stimuli  that  are  in 
themselves  beneficial  or  injurious,  but  to  stimuli  which  lead  to  bene- 
ficial or  injurious  conditions.  This  is  as  true  of  positive  as  of  negative 
reactions.  It  is  true  of  Amoeba  when  it  moves  toward  a  solid  body  that 
will  give  it  an  opportunity  to  creep  about  and  obtain  food.  It  is  true  of 
Paramecium  when  it  settles  against  solids  (even  bits  of  filter  paper), 
because  usually  such  solids  furnish  a  supply  of  bacteria.  It  is  true  of 
the  colorless  flagellate  Chytridium  and  the  white  Hydra,  when  they  move 
toward  a  source  of  light  and  thus  come  into  the  region  where  their  prey 
congregate.  There  seems  to  be  no  general  name  for  this  positive  re- 
action to  a  representative  stimulus.  In  man  we  call  various  subjective 
aspects  of  it  by  different  names,  —  foresight,  anticipation,  prudence, 
hope,  etc. 

The  fact  that  lower  as  well  as  higher  organisms  thus  react  to  repre- 
sentative stimuli  is  of  the  greatest  significance.  It  provides  the  chief 
condition  for  the  advance  of  behavior  to  higher  planes.  At  the  basis 
of  reaction  of  this  character  lies  the  simple  fact  that  a  change,  even  though 
neutral  in  its  effect,  may  cause  reaction  (p.  294).  This  taken  in  con- 
nection with  the  law  of  the  resolution  of  physiological  states  (p.  291) 
permits  the  establishment  of  a  negative  or  positive  reaction,  as  the  case 
may  require,  as  a  response  to  a  given  change.  The  way  in  which  this 
may  take  place  we  have  attempted  to  set  forth  on  page  316. 

Related  to  these  reactions  to  representative  stimuli  are  certain  other 
characteristics  distinguished  in  the  behavior  of  man  and  higher  animals. 
The  objective  side  of  memory  and  what  is  called  habit  is  shown  when 
the  behavior  of  an  organism  is  modified  in  accordance  with  past  stimuli 
received  or  past  reactions  given.  If  the  behavior  is  merely  changed  in 
a  way  that  is  not  regulatory,  as  by  fatigue,  we  do  not  call  this  memory. 
In  memory  the  reaction  is  modified  in  such  a  way  that  it  is  now  more 
adequate  to  the  conditions  to  be  met.  Habit  and  memory  in  this  ob- 
jective sense  are  clearly  seen  in  the  Crustacea,  and  in  the  low  accelous 
flatworm  Convoluta  (p.  255).  Something  of  a  similar  character  is  seen 
even  in  the  protozoan  Stentor.  After  reacting  to  a  weak  stimulus  which 
does  not  lead  to  an  injurious  one  it  ceases  to  react  when  this  stimulus 
is  repeated,  while  if  the  weak  stimulus  does  lead  to  an  injurious  one, 
the  animal  changes  its  behavior  so  as  to  react  next  time  in  a  more  effec- 
tive way;  and  it  repeats  this  more  effective  reaction  at  the  next  inci- 
dence of  the  stimulus.  Habit  and  memory,  objectively  considered, 
are  based  on  the  law  of  the  resolution  of  physiological  states  (p.  291), 
which  may  be  set  forth  in  application  to  the  present  subject  as  follows: 
If  a  given  physiological   state,  induced   by  a   stimulus,  is   repeatedly 


334  BEHAVIOR  OF   THE  LOWER   ORGANISMS 

resolved  into  a  succeeding  state,  this  resolution  becomes  easier,  and  may 
take  place  spontaneously,  so  that  the  reaction  induced  is  that  due  pri- 
marily to  the  second  physiological  state  reached.  Wherever  we  find 
this  law  in  operation,  we  have  the  ultimate  basis  from  which  habit  and 
memory  (objectively  considered)  are  developed. 

From  memory  in  the  general  sense  it  is  customary  to  distinguish 
associative  memory.  This  is  characterized  objectively  by  the  fact  that 
the  response  at  first  given  to  one  stimulus  comes,  after  a  time,  to  be 
transferred  to  another  one.  Examples  of  associative  memory  are  seen 
in  the  experiments  of  Yerkes  and  Spaulding  on  crustaceans,  described 
in  Chapter  XII.  It  may  be  pointed  out  that  the  essential  basis  for 
associative  memory  is  the  same  law  of  the  resolution  of  physiological 
states  which  we  have  set  forth  in  the  last  paragraph  as  underlying  ordi- 
nary memory.  The  physiological  condition  induced  by  the  first  stimu- 
lus (sight  of  the  screen,  in  Spaulding's  experiments)  is  regularly  re- 
solved into  that  due  to  the  second  stimulus  (food,  in  the  experiments 
just  mentioned).  After  a  time  the  resolution  becomes  spontaneous,  so 
that  the  physiological  state  primarily  due  to  the  food  is  reached  imme- 
diately after  the  introduction  of  the  screen,  even  though  no  food  is  given. 
There  seems  to  be  no  difference  in  kind,  therefore,  between  associative 
memory  and  other  sorts ;  they  are  based  on  the  same  fundamental  law. 
The  existence  of  associative  memory  has  often  been  considered  a  criterion 
of  the  existence  of  consciousness,  but  it  is  clear  that  the  process  under- 
lying it  is  as  readily  conceivable  in  terms  of  matter  and  energy  as  are  other 
physiological  processes.  Even  in  inorganic  colloids,  as  we  have  seen 
(p.  317),  the  properties  depend  on  the  past  history  of  the  colloid,  and  the 
way  in  which  it  has  reached  the  condition  in  which  it  is  now  found.  If 
this  is  conceivable  in  terms  of  matter  and  energy,  it  is  difficult  to  see  why 
the  law  of  the  readier  resolution  of  physiological  states  is  not  equally  so. 

Intelligence  is  commonly  held  to  consist  essentially  in  the  modifica- 
tion of  behavior  in  accordance  with  experience.  If  an  organism  reacts 
in  a  certain  way  under  certain  conditions,  and  continues  this  reaction 
no  matter  how  disastrous  the  effects,  we  say  that  its  behavior  is  unin- 
telligent. If  on  the  other  hand  it  modifies  its  behavior  in  such  a  way  as 
to  make  it  more  adequate,  we  consider  the  behavior  as  in  so  far  intel- 
ligent. It  is  the  "correlation  of  experiences  and  actions"  that  consti- 
tutes, as  Hobhouse  (1901)  has  put  it,  "the  precise  work  of  intelligence." 

It  appears  clear  that  we  find  the  beginnings  of  such  adaptive  changes 
of  behavior  even  in  the  Protozoa.  They  are  brought  about  through  the 
law  in  accordance  with  which  the  resolution  of  one  physiological  state 
into  another  takes  place  more  readily  after  repetition,  —  in  connection 
with  the  other  principle  that  interference  with  the  life  processes  causes 


RELATION   TO   PSYCHIC  BEHAVIOR 


335 


a  change  of  behavior.  These  laws  apparently  form  the  fundamental 
basis  of  intelligent  action.  This  fundamental  basis  then  clearly  exists 
even  in  the  Protozoa ;  it  is  apparently  coextensive  with  life.  It  is  diffi- 
cult if  not  impossible  to  draw  a  line  separating  the  regulatory  behavior 
of  lower  organisms  from  the  so-called  intelligent  behavior  of  higher 
ones ;  the  one  grades  insensibly  into  the  other.  From  the  lowest  organ- 
isms up  to  man  behavior  is  essentially  regulatory  in  character,  and  what 
we  call  intelligence  in  higher  animals  is  a  direct  outgrowth  of  the  same 
laws  that  give  behavior  its  regulatory  character  in  the  Protozoa. 

Thus  it  seems  possible  to  trace  back  to  the  lowest  organisms  some  of 
the  phenomena  which  we  know,  from  objective  evidence,  to  exist  in  the 
behavior  of  man  and  the  higher  animals,  and  which  have  received  special 
names.  It  would  doubtless  be  possible  to  extend  this  to  many  other 
phenomena.  Many  conditions  which  we  can  clearly  distinguish  in 
man  must  be  followed  back  to  a  single  common  condition  in  the  lower 
organism.  But  this  is  what  we  should  expect.  Differentiation  takes 
place  as  we  pass  upward  in  the  scale  in  these  matters  as  in  others. 
Because  we  can  trace  these  phenomena  back  to  conditions  found  in 
unicellular  forms,  it  does  not  follow  that  the  behavior  of  these  organisms 
has  as  many  factors  and  is  as  complex  as  that  of  higher  animals. 
The  facts  are  precisely  parallel  with  what  we  find  to  be  true  for  other 
functions.  Amoeba  shows  respiration,  and  all  the  essential  features  of 
respiration  in  man  can  be  traced  back  to  the  condition  in  such  an  organ- 
ism. Yet  in  man  respiration  is  an  enormously  complex  operation, 
while  in  Amoeba  it  is  of  the  simplest  character  possible  —  apparently 
little  more  than  a  mere  interdiffusion  of  gases.  In  the  case  of  behavior 
there  is  the  same  possibility  of  tracing  all  essential  features  back  to  the 
lower  organisms,  with  the  same  great  simplification  as  we  go  back. 


The  Question  of  Consciousness 


All  that  we  have  said  thus  far  in  the  present  chapter  is  independent 
of  the  question  whether  there  exist  in  the  lower  organisms  such  subjec- 
tive accompaniments  of  behavior  as  we  find  in  ourselves,  and  which 
we  call  consciousness.  We  have  asked  merely  whether  there  exist  in 
the  lower  organisms  objective  phenomena  of  a  character  similar  to  what 
we  find  in  the  behavior  of  man.  To  this  question  we  have  been  com- 
pelled to  give  an  affirmative  answer.  So  far  as  objective  evidence  goes, 
there  is  no  difference  in  kind,  but  a  complete  continuity  between  the 
behavior  of  lower  and  of  higher  organisms. 

Has  this  any  bearing  on  the  question  of  the  existence  of  conscious- 
ness in  lower  animals?     It  is  clear  that  objective  evidence  cannot  give 


336  BEHAVIOR  OF   THE   LOWER  ORGANISMS 

a  demonstration  either  of  the  existence  or  of  the  non-existence  of  con- 
sciousness, for  consciousness  is  precisely  that  which  cannot  be  perceived 
objectively.  No  statement  concerning  consciousness  in  animals  is  open 
to  verification  or  refutation  by  observation  and  experiment.  There 
are  no  processes  in  the  behavior  of  organisms  that  are  not  as  readily 
conceivable  without  supposing  them  to  be  accompanied  by  conscious- 
ness as  with  it. 

But  the  question  is  sometimes  proposed :  Is  the  behavior  of  lower 
organisms  of  the  character  which  we  should  "naturally"  expect  and 
appreciate  if  they  did  have  conscious  states,  of  undifferentiated  character, 
and  acted  under  similar  conscious  states  in  a  parallel  way  to  man  ?  Or 
is  their  behavior  of  such  a  character  that  it  does  not  suggest  to  the 
observer  the  existence  of  consciousness? 

If  one  thinks  these  questions  through  for  such  an  organism  as  Para- 
mecium, with  all  its  limitations  of  sensitiveness  and  movement,  it  appears 
to  the  writer  that  an  affirmative  answer  must  be  given  to  the  first  of  the 
above  questions,  and  a  negative  one  to  the  second.  Suppose  that  this 
animal  were  conscious  to  such  an  extent  as  its  limitations  seem  to  permit. 
Suppose  that  it  could  feel  a  certain  degree  of  pain  when  injured;  that 
it  received  certain  sensations  from  alkali,  others  from  acids,  others  from 
solid  bodies,  etc., — would  it  not  be  natural  for  it  to  act  as  it  does? 
That  is,  can  we  not,  through  our  consciousness,  appreciate  its  drawing 
away  from  things  that  hurt  it,  its  trial  of  the  environment  when  the 
conditions  are  bad,  its  attempting  to  move  forward  in  various  directions, 
till  it  finds  one  where  the  conditions  are  not  bad,  and  the  like?  To 
the  writer  it  seems  that  we  can;  that  Paramecium  in  this  behavior 
makes  such  an  impression  that  one  involuntarily  recognizes  it  as  a  little 
subject  acting  in  ways  analogous  to  our  own.  Still  stronger,  perhaps, 
is  this  impression  when  observing  an  Amoeba  obtaining  food  as  shown 
in  Figs.  19  and  21.  The  writer  is  thoroughly  convinced,  after  long  study 
of  the  behavior  of  this  organism,  that  if  Amoeba  were  a  large  animal,  so 
as  to  come  within  the  everyday  experience  of  human  beings,  its  be- 
havior would  at  once  call  forth  the  attribution  to  it  of  states  of  pleasure 
and  pain,  of  hunger,  desire,  and  the  like,  on  precisely  the  same  basis 
as  we  attribute  these  things  to  the  dog.  This  natural  recognition  is 
exactly  what  Munsterberg  (1900)  has  emphasized  as  the  test  of  a 
subject.  In  conducting  objective  investigations  we  train  ourselves  to 
suppress  this  impression,  but  thorough  investigation  tends  to  restore  it 
stronger  than  at  first. 

Of  a  character  somewhat  similar  to  that  last  mentioned  is  another 
test  that  has  been  proposed  as  a  basis  for  deciding  as  to  the  conscious- 
ness of  animals.     This  is  the  satisfactoriness  or  usefulness  of  the  concept 


RELATION   TO   PSYCHIC   BEHAVIOR  337 

of  consciousness  in  the  given  case.  We  do  not  usually  attribute  con- 
sciousness to  a  stone,  because  this  would  not  assist  us  in  understanding 
or  controlling  the  behavior  of  the  stone.  Practically  indeed  it  would 
lead  us  much  astray  in  dealing  with  such  an  object.  On  the  other 
hand,  we  usually  do  attribute  consciousness  to  the  dog,  because  this  is  use- 
ful ;  it  enables  us  practically  to  appreciate,  foresee,  and  control  its  actions 
much  more  readily  than  we  could  otherwise  do  so.  If  Amoeba  were 
so  large  as  to  come  within  our  everyday  ken,  I  believe  it  beyond  ques- 
tion that  we  should  find  similar  attribution  to  it  of  certain  states  of  con- 
sciousness a  practical  assistance  in  foreseeing  and  controlling  its  behavior. 
Amoeba  is  a  beast  of  prey,  and  gives  the  impression  of  being  controlled 
by  the  same  elemental  impulses  as  higher  beasts  of  prey.  If  it  were  as 
large  as  a  whale,  it  is  quite  conceivable  that  occasions  might  arise  when 
the  attribution  to  it  of  the  elemental  states  of  consciousness  might  save 
the  unsophisticated  human  being  from  the  destruction  that  would  result 
from  the  lack  of  such  attribution.  In  such  a  case,  then,  the  attribution 
of  consciousness  would  be  satisfactory  and  useful.  In  a  small  way  this 
is  still  true  for  the  investigator  who  wishes  to  appreciate  and  predict 
the  behavior  of  Amoeba  under  his  microscope. 

But  such  impressions  and  suggestions  of  course  do  not  demonstrate 
the  existence  of  consciousness  in  lower  organisms.  Anv  belief  on  this 
matter  can  be  held  without  conflict  with  the  objective  facts.  All  that 
experiment  and  observation  can  do  is  to  show  us  whether  the  behavior 
of  lower  organisms  is  objectively  similar  to  the  behavior  that  in  man  is 
accompanied  by  consciousness.  If  this  question  is  answered  in  the 
affirmative,  as  the  facts  seem  to  require,  and  if  we  further  hold,  as  is 
commonly  held,  that  man  and  the  lower  organisms  are  subdivisions  of 
the  same  substance,  then  it  may  perhaps  be  said  that  objective  investi- 
gation is  as  favorable  to  the  view  of  the  general  distribution  of  conscious- 
ness throughout  animals  as  it  could  well  be.  But  the  problem  as  to  the 
actual  existence  of  consciousness  outside  of  the  self  is  an  indeterminate 
one;  no  increase  of  objective  knowledge  can  ever  solve  it.  Opinions 
on  this  subject  must  then  be  largely  dominated  by  general  philosophical 
considerations,  drawm  from  other  fields. 

LITERATURE  XX 

Consciousness  in  Lower  Animals 

Claparede,  1901,  1905 ;  Titchener,  1902 ;  Minot,  1902 ;  Munsterberg, 
1900;  Verworn.  1889;  Bethe,  1898;  Yerkes,  1905,  1905  a\  Jordan,  1905; 
v.  Uexkull,  1900  b,  1902  ;  Wasmann,  1901,  1905  ;  Lukas,  1905. 


CHAPTER  XXI 

BEHAVIOR  AS  REGULATION,  AND  REGULATION  IN  OTHER  FIELDS 

i.   Introductory 

Everywhere  in  the  study  of  life  processes  we  meet  the  puzzle  of 
regulation.  Organisms  do  those  things  that  advance  their  welfare.  If 
the  environment  changes,  the  organism  changes  to  meet  the  new  condi- 
tions. If  the  mammal  is  heated  from  without,  it  cools  from  within ;  if 
it  is  cooled  from  without,  it  heats  from  within,  maintaining  the  tempera- 
ture that  is  to  its  advantage.  The  dog  which  is  fed  a  starchy  diet  pro- 
duces digestive  juices  rich  in  enzymes  that  digest  starch ;  while  under  a 
diet  of  meat  it  produces  juices  rich  in  proteid-digesting  substances. 
When  a  poison  is  injected  into  a  mouse,  the  mouse  produces  substances 
which  neutralize  this  poison.  If  a  part  of  the  organism  is  injured,  a 
rearrangement  of  material  follows  till  the  injury  is  repaired.  If  a  part 
is  removed,  it  is  restored,  or  the  wound  is  at  least  closed  up  and  healed, 
so  that  the  life  processes  may  continue  without  disturbance.  Regulation 
constitutes  perhaps  the  greatest  problem  of  life.  How  can  the  organism 
thus  provide  for  its  own  needs?  To  put  the  question  in  the  popular 
form,  How  does  it  know  what  to  do  when  a  difficulty  arises?  It  seems 
to  work  toward  a  definite  purpose.  In  other  words,  the  final  result  of 
its  action  seems  to  be  present  in  some  way  at  the  beginning,  determin- 
ing what  the  action  shall  be.  In  this  the  action  of  living  tilings  appears 
to  contrast  with  that  of  things  inorganic.  It  is  regulation  of  this  charac- 
ter that  has  given  rise  to  theories  of  vitalism.  The  principles  control- 
ling the  life  processes  are  held  by  these  theories  to  be  of  a  character 
essentially  different  from  anything  found  in  the  inorganic  world.  This 
view  has  found  recent  expression  in  the  works  of  Driesch  (1901,  1903). 

2.   Regulation  in  Behavior 

Nowhere  is  regulation  more  striking  than  in  behavior.  Indeed,  the 
processes  in  this  field  have  long  served  as  the  prototype  for  regulatory 
action.  The  organism  moves  and  reacts  in  ways  that  are  advantageous 
to  it.     If  it  gets  into  hot  water,  it  takes  measures  to  get  out  again,  and 

338 


REGULATION  IN  BEHAVIOR  339 

the  same  is  true  if  it  gets  into  excessively  cold  water.  If  it  enters  an 
injurious  chemical  solution,  it  at  once  changes  its  behavior  and  escapes. 
If  it  lacks  material  for  its  metabolic  processes,  it  sets  in  operation  move- 
ments which  secure  such  material.  If  it  lacks  oxygen  for  respiration, 
it  moves  to  a  region  where  oxygen  is  found.  If  it  is  injured,  it  flees  to 
safer  regions.  In  innumerable  details  it  does  those  things  that  are  good 
for  it.  It  is  plain  that  behavior  depends  largely  on  the  needs  of  the 
organism,  and  is  of  such  a  nature  as  to  satisfy  these  needs.  In  other 
words,  it  is  regulatory. 

Behavior  is  merely  a  collective  name  for  the  most  obvious  and  most 
easily  studied  of  the  processes  of  the  organism,  and  it  is  clear  that  these 
processes  are  closely  connected  with,  and  are  indeed  outgrowths  from, 
the  more  recondite  internal  processes.  There  is  no  reason  for  supposing 
them  to  follow  laws  different  from  those  of  the  other  life  processes,  or 
for  holding  that  regulation  in  behavior  is  of  a  different  character  from 
that  found  elsewhere.  But  nowhere  else  is  it  possible  to  perceive  so 
clearly  how  regulation  occurs.  In  the  behavior  of  the  lowest  organisms 
we  can  see  not  only  what  the  animal  does,  but  precisely  how  this  happens 
to  be  regulatory.  The  method  of  regulation  lies  open  before  us.  This 
method  is  of  such  a  character  as  to  suggest  the  possibility  of  its  general 
applicability  to  life  processes.  In  the  present  chapter  we  shall  attempt 
to  sum  up  the  essential  points  in  regulation  as  shown  in  behavior,  and 
to  make  some  suggestions  as  to  its  possible  application  to  other  fields. 

A.   Factors  in  Regulation  in  the  Behavior  of  Lower  Organisms 

In  the  lower  organisms,  where  we  can  see  just  how  regulation  occurs, 
the  process  is  as  follows:  Anything  injurious  to  the  organism  causes 
changes  in  its  behavior.  These  changes  subject  the  organism  to  new 
conditions.  As  long  as  the  injurious  condition  continues,  the  changes 
of  behavior  continue.  The  first  change  of  behavior  may  not  be  regu- 
latory, nor  the  second,  nor  the  third,  nor  the  tenth.  But  if  the  changes 
continue,  subjecting  the  organism  successively  to  all  possible  different 
conditions,  a  condition  will  finally  be  reached  that  relieves  the  organism 
from  the  injurious  action,  provided  such  a  condition  exists.  Thereupon 
the  changes  in  behavior  cease,  and  the  organism  remains  in  the  favor- 
able condition.  The  movements  of  the  organism  when  stimulated  are 
such  as  to  subject  it  to  various  conditions,  one  of  which  is  selected. 

This  method  of  regulation  is  found  in  its  purest  form  in  unicellular 
organisms.  But,  as  we  have  seen  in  preceding  pages,  it  occurs  also  in 
higher  organisms,  and  indeed  is  found  in  a  less  primitive  form  through- 
out the  animal  series,  up  to  and  including  man.     It  is  commonly  spoken 


340  BEHAVIOR   OF   THE  LOWER   ORGAXISMS 

of  as  behavior  by  "trial  and  error."  In  connection  with  this  method  of 
behavior,  three  questions  arise,  which  are  fundamental  for  the  theory 
of  regulation.  The  first  is  as  follows :  How  is  it  determined  what  shall 
cause  the  changes  in  behavior  resulting  in  new  conditions?  Why  does 
the  organism  change  its  behavior  under  certain  conditions,  not  under 
others?  Second,  how  does  it  happen  that  such  movements  are  pro- 
duced as  result  in  more  favorable  conditions  ?  Third,  how  is  the  more 
favorable  condition  selected?  What  it  this  selection  and  what  does  it 
imply  ? 

Our  first  and  third  questions  may  indeed  be  condensed  into  one, 
which  involves  the  essence  of  regulation.  Why  does  the  organism 
choose  certain  conditions  and  reject  others?  This  selection  of  the  fa- 
vorable conditions  and  rejection  of  the  unfavorable  ones  presented  by 
the  movements  is  perhaps  the  fundamental  point  in  regulation. 

It  is  often  maintained  that  this  selection  is  precisely  personal  or  con- 
scious choice,  and  that  the  behavior  cannot  be  explained  without  this 
factor.  Personal  choice  it  evidently  is,  and  in  man  it  is  often  conscious 
choice ;  whether  it  is  conscious  in  other  animals  we  do  not  know.  But 
in  any  case  this  does  not  remove  it  from  the  necessity  for  analysis. 
Whether  conscious  or  unconscious,  choice  must  be  determined  in  some 
way,  and  it  is  the  province  of  science  to  inquire  as  to  how  this  determina- 
tion occurs.  To  say  that  rejection  is  due  to  pain,  acceptance  to  pleasure 
or  to  other  conscious  states,  does  not  help  us,  for  we  are  then  forced  to 
inquire  why  pain  occurs  under  certain  circumstances,  pleasure  under 
others.  Surely  this  is  not  a  mere  haphazard  matter.  There  must  be 
some  difference  in  the  conditions  to  induce  these  differences  in  the  con- 
scious states  (if  they  exist),  and  at  the  same  time  to  determine  the 
differences  in  behavior.  We  are  therefore  thrown  back  upon  the  objec- 
tive processes  occurring.  Why  are  certain  conditions  accepted,  others 
rejected  ? 

Let  us  examine  one  or  two  of  the  simplest  cases  of  such  regulatory 
selection.  The  green  infusorian  Paramecium  bursaria  requires  oxygen 
for  its  metabolic  processes.  While  swimming  about  it  comes  to  a  region 
where  oxygen  is  lacking.  Thereupon  it  changes  its  behavior,  turns  away, 
and  goes  in  some  other  direction.  The  white  Paramecium  caudatum 
does  the  same,  and  so  also  do  many  bacteria;  they  likewise  require  oxy- 
gen for  their  metabolic  processes.  All  reject  a  region  without  oxygen. 
The  green  Paramecium  bursaria  comes  to  a  dark  region.  The  water 
contains  plenty  of  oxygen,  hence  the  metabolic  processes  are  proceeding 
uninterruptedly,  and  passing  into  darkness  does  not  interfere  with  them. 
The  animal  does  not  change  its  behavior,  but  enters  the  dark  region 
without  hesitation.     Later  the  oxygen  in  the  water  has  become  nearly 


REGULATION  IN  BEHAVIOR  341 

exhausted.  The  animal  is  again  swimming  about  in  the  light,  and  the 
green  chlorophyll  bodies  winch  it  contains  are  producing  a  little  oxygen 
which  the  infusorian  uses  in  its  metabolic  processes.  Now  it  comes 
again  to  a  dark  region.  In  the  darkness  the  production  of  oxygen  by 
the  green  bodies  ceases;  they  no  longer  supply  the  metabolic  processes 
with  this  necessary  factor.  Now  we  find  that  the  infusorian  rejects,  the 
darkness  and  turns  in  another  direction.  The  white  Paramecium  cau- 
datum  does  not  do  this,  nor  do  the  colorless  bacteria.  Possessing  no 
chlorophyll,  they  receive  no  more  oxygen  in  the  light  than  in  the 
darkness,  and  they  pass  into  darkness  as  readily  as  into  light.  But 
many  colored  bacteria  do  reject  the  darkness.  They  require  light  in 
certain  other  metabolic  processes,  —  in  their  assimilation  of  inorganic 
compounds,  —  and  when  they  come  to  the  boundary  between  light  and 
darkness,  they  return  into  the  light.  Most  bacteria  reject  regions  con- 
taining no  oxygen,  as  we  have  seen.  But  in  certain  bacteria,  oxygen  is 
not  required  for  the  metabolic  processes;  on  the  contrary,  it  impedes 
them.  These  bacteria  reject  regions  containing  oxygen,  swimming  back 
into  the  light.  In  some  cases  among  unicellular  organisms  the  relation 
of  behavior  to  the  metabolic  processes  is  exceedingly  precise.  Thus, 
Engelmann  (1882  a)  proved  that  in  Bacterium  (or  Chromatium)  photo- 
nic! ricum  the  ultra-red  and  the  yellow-orange  rays  are  those  most  favor- 
able to  the  metabolic  processes  (assimilation  of  carbon  dioxide,  etc.). 
When  a  microspectrum  is  thrown  on  these  bacteria,  they  are  found  to 
react  in  such  a  way  as  to  collect  in  precisely  the  ultra-red  and  the  yellow- 
orange.  The  reaction  consists  in  a  change  of  behavior,  —  a  reversal  of 
movement,  —  at  the  moment  of  passing  from  the  ultra-red  or  the  yel- 
low-orange to  any  other  part  of  the  spectrum.  At  that  same  instant 
the  metabolic  processes  of  course  suffer  interference.  Bacteria  are  not 
in  nature  subjected  to  pure  spectral  colors  in  bands,  so  that  there  has 
been  no  opportunity  for  the  production  of  this  correspondence  between 
behavior  and  favorable  conditions,  through  the  natural  selection  of  vary- 
ing individuals. 

In  all  these  cases  the  behavior  depends  upon  the  metabolic  processes, 
and  is  of  such  a  character  as  to  favor  them.  Throughout  the  present 
volume  we  have  found  similar  relations  to  hold  for  all  sorts  of  organisms. 
We  find  even  that  when  the  metabolic  processes  of  a  given  individual 
change,  the  behavior  changes  in  a  corresponding  way. 

Why  does  the  bacterium  or  infusorian  change  its  behavior  and  shrink 
back  from  the  darkness  or  the  region  containing  no  oxgyen  ?  As  a  mat- 
ter of  fact,  it  needs  the  light  or  the  oxygen  in  its  metabolic  processes, 
and  it  does  not  shrink  back  from  their  absence  unless  it  does  need  them. 
But  we  have  no  reason  to  attribute  to  the  bacterium  anything  like  a 


342  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

knowledge  or  idea  of  that  relation.  We  do  not  need  any  purpose  or 
idea  in  the  mind  of  the  organism,  or  any  "psychoid"  or  entelechy,  to 
account  for  the  change  of  behavior,  for  an  adequate  objective  cause 
exists.  We  know  experimentally  that  the  darkness  or  the  lack  of  oxygen 
interferes  with  the  metabolic  processes.  This  very  interference  is  then 
evidently  the  cause  of  the  change  of  behavior.  The  organism  is  known 
to  be  the  seat  of  varied  processes,  proceeding  with  a  certain  energy. 
When  there  is  interference  with  these  processes,  the  energy  overflows 
into  other  channels,  resulting  in  changes  in  behavior.  This  statement 
is  a  formulation  of  the  facts  determined  by  observation  and  experiment 
in  the  most  diverse  organisms.  It  is  illustrated  on  almost  every  page 
of  the  present  work. 

In  the  lower  organisms  the  processes  of  metabolism  are  the  chief 
ones  occurring,  and  behavior  is  largely  determined  with  reference  to 
them.  In  higher  organisms  these  usually  retain  their  commanding  role, 
but  an  immense  number  of  coordinated  and  subsidiary  processes  also 
occur,  and  changes  in  behavior  may  be  induced  by  interference  with  any 
of  these. 

The  answer  to  our  first  question  is  then  as  follows :  The  organism 
changes  its  behavior  as  a  result  of  interference  or  disturbance  in  its 
physiological  processes. 

Our  second  question  was :  How  does  it  happen  that  such  movements 
are  produced  as  bring  about  more  favorable  conditions  ?  This  question 
we  have  already  answered,  so  far  as  lower  organisms  are  concerned,  in 
our  general  statement  on  page  339.  The  organism  does  not  go  straight 
for  a  final  end.  It  merely  acts,  —  in  all  sorts  of  ways  possible  to  it,  — ■ 
resulting  in  repeated  changes  of  the  environmental  conditions.  The 
fundamental  fact  must  be  remembered  that  the  life  processes  depend 
upon  internal  and  external  conditions,  and  are  favored  by  conditions 
that  are  rather  generally  distributed  throughout  the  environment  of  or- 
ganisms. If  there  were  no  favorable  conditions  attainable,  of  course  no 
change  of  behavior  could  attain  them.  But  the  favorable  conditions 
actually  exist,  and  if  the  changes  of  behavior  continue,  subjecting  the 
organism  to  all  possible  different  conditions,  a  condition  will  finally  be 
reached  that  is  favorable  to  the  life  processes.  Often  only  a  slight  change 
of  behavior  is  required  in  order  to  bring  about  favorable  conditions.  If 
an  organism  swims  suddenly  into  a  heated  area,  almost  any  change  in 
the  direction  of  movement  is  likely  to  restore  the  conditions  previously 
existing.  Adjustment,  then,  is  reached  by  repeated  changes  of  move- 
ment. 

Our  third  question  was:  How  does  the  organism  select  the  more 
favorable  condition  thus  reached?     This  question  now  answers  itself. 


REGULATION  IN  BEHAVIOR 


343 


It  was  the  interference  with  the  physiological  processes  that  caused  the 
changes  in  behavior.  As  soon  therefore  as  this  interference  ceases,  there 
is  no  further  cause  for  change.  The  organism  selects  and  retains  the 
favorable  condition  reached,  merely  by  ceasing  to  change  its  behavior 
when  interference  ceases. 

Thus  in  the  lowest  organisms  we  find  regulation  occurring  on  the 
basis  of  the  three  following  facts :  — 

i.    Definite  internal  processes  are  occurring  in  organisms. 

2.  Interference  with  these  processes  causes  a  change  of  behavior  and 
varied  movements,  subjecting  the  organism  to  many  different  conditions. 

3.  One  of  these  conditions  relieves  the  interference  with  the  internal 
processes,  so  that  the  changes  in  behavior  cease. 

It  is  clear  that  regulation  taking  place  in  this  way  does  not  require 
that  the  end  or  purpose  of  the  action  shall  function  in  any  way  as  part 
of  its  cause,  as  is  held  in  various  vitalistic  theories.  There  is  no  evi- 
dence that  a  final  aim  is  guiding  the  organism.  None  of  the  factors 
above  mentioned  appear  to  include  anything  differing  in  essential  prin- 
ciple from  such  methods  of  action  as  we  find  in  the  inorganic  world. 

Now  an  additional  factor  enters  the  problem.  By  the  process  which 
we  have  just  considered,  the  organism  reaches  in  time  a  movement  that 
brings  relief  from  the  interfering  conditions.  This  relieving  response 
becomes  fixed  through  the  operation  of  the  law  of  the  readier  resolu- 
tion of  physiological  states  as  a  result  of  repetition  (Chapter  XVI,  Sec- 
tion 10).  After  reaching  the  relieving  response  a  number  of  times  by  a 
repeated  succession  of  movements,  a  recurrence  of  the  interfering  con- 
dition induces  more  quickly  the  relieving  response,  and  in  time  this 
becomes  the  immediate  reaction  to  this  interfering  condition. 

It  is  in  this  second  stage  of  the  process,  when  the  relieving  response 
has  become  set  through  the  law  of  the  readier  resolution  of  physiological 
states  by  repetition,  that  an  end  or  purpose  seems  to  dominate  the  be- 
havior. This  end  or  purpose  of  course  actually  exists,  as  a  subjective 
state  called  an  idea,  in  man.  Whether  any  such  subjective  state  exists 
in  the  lower  organism  that  has  gone  through  the  process  just  sketched, 
of  course  we  do  not  know.  But  some  objective  phenomenon,  as  a  tran- 
sient physiological  state,  would  seem  to  be  required  in  the  lower  animal, 
corresponding  to  the  objective  physiological  accompaniment  of  the  idea 
in  man.  The  behavior  in  this  stage  is  that  which,  in  its  higher  reaches 
at  least,  has  been  called  intelligent. 

But  so  far  as  the  objective  occurrences  are  concerned,  there  would 
seem  to  be  nothing  in  this  later  stage  of  the  behavior  involving  any- 
thing different  in  essential  principle  from  what  we  find  in  the  inorganic 
world.    The  only  additional  factor  is  the  law  of  the  readier  resolution  of 


344  BEHAVIOR   OF   THE  LOWER   ORGANISMS 

physiological  states  after  repetition.  While  possibly  our  statement  of  this 
law  may  not  be  entirely  adequate,  there  would  seem  to  be  nothing  im- 
plied by  it  that  is  specifically  vital,  in  the  sense  that  it  differs  in  essential 
principle  from  the  methods  of  action  seen  in  the  inorganic  world.  This 
law  of  the  readier  resolution  of  physiological  states  after  repetition  pre- 
sents indeed  many  analogies  with  various  chains  of  physical  and  chemi- 
cal action.1  It  certainly  by  no  means  requires  in  itself  the  action  of  any 
"final  cause,"  —  that  is,  of  an  entity  that  is  at  the  same  time  purpose 
and  cause.  On  the  other  hand,  it  undoubtedly  does  produce  that  type 
of  behavior  which  has  given  rise  to  the  conception  of  the  purpose  acting 
as  cause.  This  conception  is  in  itself  of  course  a  correct  one,  so  far  as 
we  mean  by  a  purpose  an  actual  physiological  state  of  the  organism, 
determining  behavior  in  the  same  manner  as  other  factors  determine  it. 
But  such  a  physiological  state  (subjectively  a  purpose)  is  a  result  of  a 
foregoing  objective  cause,  and  acts  to  produce  an  effect  in  the  same  way 
as  any  other  link  in  the  causal  chain.  It  would  seem  therefore  to  pre- 
sent no  basis  for  theories  of  vitalism,  so  far  as  these  depend  on  anything 
like  the  action  of  final  causes. 

That  regulation  takes  place  in  the  behavior  of  many  animals  in  the 
manner  above  sketched  may  be  affirmed  as  a  clearly  established  fact, 
and  it  seems  to  be  perhaps  the  only  intelligible  way  in  which  regulatory 
behavior  could  be  developed  in  a  given  individual. 

But  we  are,  of  course,  confronted  by  the  fact  that  many  individuals 
are  provided  at  birth  with  definite  regulatory  methods  of  reaction  to  cer- 
tain stimuli.  In  these  cases  the  animal  is  not  compelled  to  go  through 
the  process  of  performing  varied  movements,  with  subsequent  fixation  of 
the  successful  movement.     How  are  such  cases  to  be  accounted  for? 

If  the  regulatory  method  of  reaction  acquire!  through  the  process 
sketched  in  the  preceding  paragraphs  could  be  inherited,  there  would  of 
course  be  no  difficulty  in  accounting  for  such  congenital  regulatory  re- 
actions. In  Protozoa  this  is  apparently  the  real  state  of  the  case ;  there 
appears  to  be  no  reason  why  the  products  of  reproduction  by  division 
should  not  inherit  the  properties  of  the  individual  that  divides,  however 
these  properties  were  attained.  But  in  the  Metazoa  such  inheritance  of 
acquirements  presents  great  theoretical  difficulties,  and  has  not  been  ex- 
perimentally demonstrated  to  occur,  though  it  is  perhaps  too  early  to  con- 
sider the  matter  as  yet  out  of  court.  If  such  inheritance  does  not  occur, 
the  existence  of  congenital  definite  regulatory  reactions  would  seem 
explicable  only  on  the  basis  of  the  natural  selection  of  individuals  having 
varying  methods  of  reaction,  unless  we  are  to  adopt  the  theories  of  vital- 
ism.    In  the  method  we  have  sketched  above,  a  certain  reaction  that  is 

1  See  note,  page  317. 


REGULATION  IN  BEHAVIOR  345 

regulatory  is  selected,  through  the  operation  of  physiological  laws,  from 
among  many  performed  by  the  same  individual.  In  natural  selection 
the  same  reaction  is  selected  from  among  many  performed  by  different 
individuals  —  in  both  cases  because  it  is  regulatory  —  because  it 
assists  the  life  processes  of  the  organism.  The  two  factors  must  then 
work  together  and  produce  similar  results.1  In  both,  the  essential  point 
is  a  selection  from  among  varied  activities. 

We  must  here  notice  the  fact  that  we  often  find  in  organisms  be- 
havior that  is  not  regulatory.  How  are  we  to  account  for  this  ?  With- 
out going  into  details,  it  is  clear  that  there  are  a  number  of  factors  that 
would  produce  this  result.  First,  interference  with  the  life  processes  is 
not  the  only  cause  of  reaction.  The  organism  is  composed  of  matter 
that  is  subject  to  the  usual  laws  of  physics  and  chemistry.  External 
agents  may  of  course  act  on  this  matter  directly,  causing  changes  in 
movement  that  are  not  regulatory.  Second,  the  organism  can  perform 
only  those  movements  which  its  structure  permits.  Often  none  of  these 
movements  can  produce  conditions  that  relieve  the  existing  interference 
with  the  life  processes.  Then  the  organism  can  only  try  them,  without 
regulatory  results,  and  die  (see,  for  example,  such  a  case  in  the  flatworm, 
p.  244).  Further,  certain  responses  may  have  become  fixed,  in  the  way 
described  above,  because  under  usual  conditions  they  produce  adjust- 
ment. Now  if  the  conditions  change,  the  organism  still  responds  by 
the  fixed  reaction,  and  this  may  no  longer  be  regulatory.  The  organ- 
ism may  then  be  destroyed  before  a  new  regulatory  reaction  can 
be  developed  by  selection  from  varied  movements.  This  condition  of 
affairs  is  of  course  often  observed. 

All  together,  the  regulatory  character  of  behavior  as  found  in  many 
animals  seems  intelligible  in  a  perfectly  natural,  directly  causal  way,  on 
the  basis  of  the  principles  brought  out  above.  We  may  summarize  these 
principles  as  (1)  the  selection  through  varied  movements  of  conditions 
not  interfering  with  the  physiological  processes  of  the  organism  ("trial 
and  error");  (2)  the  fixation  of  the  adaptive  movements  through  the 
law  of  the  readier  resolution  of  physiological  states  after  repetition. 

3.    Regulation  in  Other  Fields 

Is  it  possible  that  individual  regulation  in  other  fields  is  based  on 
the  same  principles  that  we  have  set  forth  above  for  behavior?  Bodily 
movement  is  only  one  of  the  many  activities  that  vary,  and  variations 
of  any  of  the  organic  activities  may  impede  or  assist  the  physiological 

1  For  a  discussion  of  the  relation  of  these  two  factors,  see  Chapter  XIX. 


346  BEHAVIOR   OF  THE  LOWER   ORGANISMS 

processes  of  the  organism.  Is  it  possible  that  interference  with  the  physio- 
logical processes  may  induce  changes  in  other  activities,  —  in  chemical 
processes,  in  growth,  and  the  like,  —  and  that  one  of  these  activities  is 
selected,  as  in  behavior,  through  the  fact  that  it  relieves  the  interference 
that  caused  the  change  ? 

There  is  some  evidence  for  this  possibility.  Let  us  look,  for  example, 
at  regulative  changes  in  the  chemical  activity  of  the  organism,  such  as 
we  see  in  the  acclimatization  to  poisons,  in  the  responses  to  changes  in 
temperature,  or  in  the  adaptation  of  the  digestive  juices  to  the  food. 
What  is  the  material  from  which  the  regulative  conditions  may  be  se- 
lected? One  of  the  general  results  of  modern  physical  chemistry  is 
expressed  by  Ostwald  (1902,  p.  366)  as  follows:  "In  a  given  chemical 
structure  all  processes  that  are  so  much  as  possible,  are  really  taking 
place,  and  they  lead  to  the  formation  of  all  substances  that  can  occur 
at  all."  Some  of  these  processes  are  taking  place  so  slowly  that  they 
escape  usual  observation ;  we  notice  only  those  that  are  conspicuous. 
But  in  its  enzymes  the  body  possesses  the  means  (as  Ostwald  sets  forth) 
of  hastening  any  of  these  processes  and  delaying  others,  so  that  the  gen- 
eral character  of  the  action  shall  be  determined  by  the  more  rapid  pro- 
cess. Such  enzymes  are  usually  present  in  the  body  in  inactive  forms 
(zymogens),  which  may  be  transformed  into  active  enzymes  by  slight 
chemical  changes,  thus  altering  fundamentally  the  course  of  the  chemi- 
cal processes  in  the  organisms. 

It  is  evident,  then,  that  the  organism  has  presented  to  it,  by  the  condi- 
tion just  sketched,  unlimited  possibilities  for  the  selection  of  different 
chemical  processes.  The  body  is  a  great  mass  of  the  most  varied  chemi- 
cals, and  in  this  mass  thousands  of  chemical  processes,  in  every  direction, 
—  all  those  indeed  that  are  possible,  —  are  occurring  at  all  times.  There 
is  then  no  difficulty  as  to  the  sufficiency  of  the  material  presented  for 
selection,  if  some  means  may  be  found  for  selecting  it. 

Further,  it  is  known  that  interference  with  the  physiological  pro- 
cesses does  result  in  many  changes  in  the  internal  activities  of  the  organ- 
ism, as  well  as  in  its  external  movements.  Intense  injurious  stimula- 
tion causes  not  merely  excess  movements  of  the  body  as  a  whole,  but 
induces  marked  changes  in  circulation,  in  respiration,  in  temperature, 
in  digestive  processes,  in  excretion,  and  in  other  ways.  Such  marked 
internal  changes  involve,  and  indeed  are  constituted  by,  alterations  of 
profound  character  in  the  chemical  processes  of  the  organism.  These 
chemical  changes  are  sometimes  demonstrated  by  the  production  of  new 
chemicals  under  such  circumstances.  Furthermore,  it  is  clear  that  the 
internal  changes  due  to  interference  with  the  physiological  processes  are 
not  stereotyped  in  character,  but  varied.     Under  violent  injurious  stimu- 


REGULATION  IN  BEHAVIOR  347 

lation,  respiration  becomes  for  a  time  rapid,  then  is  almost  suspended. 
The  heart  beats  for  a  time  furiously,  then  feebly,  and  there  is  similar 
variation  in  other  internal  symptoms. 

Thus  it  seems  clear  that  interference  with  the  life  processes  does 
produce  varied  activities  in  other  ways  than  in  bodily  movements ;  and 
that  among  these  it  results  in  varied  chemical  processes.  There  is  then 
presented  opportunity  for  regulation  to  occur  in  the  same  way  as  in 
behavior.  Certain  of  the  processes  occurring  relieve  the  disturbance  of 
the  physiological  functions.  There  results  a  cessation  of  the  changes. 
In  other  words,  a  certain  process  is  selected  through  the  fact  that  it  does 
relieve.  It  is  well  known,  through  the  work  of  Pawlow  (1898),  that  the 
adaptive  changes  in  the  activities  of  the  digestive  glands,  fitting  the 
digestive  juices  to  the  food  taken,  do  not  occur  at  once  and  completely 
under  a  given  diet,  but  are  brought  about  gradually.  As  the  dog  is 
continued  on  a  diet  of  bread,  the  pancreatic  juice  becomes  more  and 
more  adapted  to  the  digestion  of  starch.  This  slow  adaptation  is  of 
course  what  should  be  expected  if  the  process  occurs  in  anything  like 
the  manner  we  have  sketched. 

At  a  later  stage,  if  the  laws  of  these  processes  are  the  same  as  those 
for  behavior,  there  will  be  present  certain  fixed  methods  of  chemical 
response,  by  which  the  organism  reacts  to  certain  sorts  of  stimulation. 
That  the  law  of  the  readier  resolution  of  physiological  states  after  repe- 
tition holds  in  this  field,  is  clearly  indicated  by  the  work  of  Pawlow.  He 
found  that  the  pancreas  under  a  uniform  diet  does  tend  to  acquire  a 
fixed  method  of  reaction  to  the  introduction  of  the  food,  that  is  not 
easily  changed.  In  the  dog  which  has  digested  starch  for  a  month,  the 
pancreatic  juice  is  not  readily  changed  back  to  that  adapted  to  the  diges- 
tion of  meat.  As  a  result,  definite  organs  will  in  the  course  of  time  have 
left  open  to  them  only  certain  limited  possibilities  of  variation  —  due 
to  the  development  of  something  corresponding  to  the  "action  system" 
in  behavior.  Thus,  in  the  pancreas,  there  will  not  exist  unlimited  possi- 
bilities as  to  the  chemical  changes  that  may  occur.  Its  "action  system" 
will  be  limited  perhaps  to  the  production  of  varied  quantities  of  a  cer- 
tain set  of  enzymes,  —  amylopsin,  trypsin,  etc.  The  proper  selection 
of  these  few  possibilities  will  then  occur  by  the  method  sketched.  When 
digestion  is  disturbed  by  food  that  is  not  well  digested,  variations  in 
the  production  of  the  different  enzymes  will  be  set  in  train,  and  one  of 
these  will  in  time  relieve  the  difficulty,  through  the  more  complete  diges- 
tion of  the  food.  Thereupon  the  variations  will  cease,  since  their  cause 
has  disappeared.  By  still  more  complete  fixation  of  the  chemical  re- 
sponse, through  the  law  of  the  readier  resolution  of  physiological  states 
after  repetition,  or  the  analogue  of  this  law,  an  organ  or  organism  may 


348  BEHAVIOR   OF   THE   LOWER   ORGANISMS 

largely  lose  its  power  of  varying  its  chemical  behavior  and  thus  be 
unable  to  meet  new  conditions  in  a  regulative  way.  A  condition  com- 
parable to  the  production  of  a  fixed  reflex  in  behavior  will  result. 

It  is  perhaps  more  difficult  to  apply  the  method  of  regulation  above 
set  forth  to  processes  of  growth  and  regeneration.  Yet  there  is  no  logi- 
cal difficulty  in  the  way.  The  only  question  would  be  that  of  fact,  — 
whether  the  varied  growth  processes  necessary  do,  primitively,  occur 
under  conditions  that  interfere  with  the  physiological  processes.  When 
a  wound  is  made  or  an  organ  removed,  is  the  growth  process  which 
follows  always  of  a  certain  stereotyped  character,  or  are  there  variations  ? 
It.  is  well  known,  of  course,  that  the  latter  is  the  case.  In  the  regenera- 
tion of  the  earthworm,  Morgan  (1897)  finds  great  variation;  he  says 
that  in  trying  many  experiments,  one  finds  that  what  ninety-nine  worms 
cannot  do  in  the  way  of  regeneration,  the  one  hundredth  can.  The 
very  great  variations  in  the  results  of  operations  on  eggs  and  young 
stages  of  animals  are  well  known.  Removal  of  an  organ  is  known  to 
produce  great  disturbance  of  most  of  the  processes  in  the  organism,  and 
among  others  in  the  process  of  growth. 

It  appears  not  impossible  then  that  regulation  may  be  brought  about 
in  growth  processes  in  accordance  with  the  same  principles  as  in  be- 
havior. A  disturbance  of  the  physiological  processes  results  in  varied 
activities,  and  among  these  are  varied  growth  activities.  Some  of  these 
relieve  the  disturbance;  the  variation  then  ceases  and  these  processes 
are  continued.  In  any  given  highly  organized  animal  or  plant  the  dif- 
ferent possibilities  of  growth  will  have  become  decidedly  limited ;  and  it 
is  only  from  this  limited  number  of  possibilities  that  selections  can  be 
made.  In  some  cases,  by  the  fixation  of  certain  processes  through  the 
analogue  of  the  law  of  the  readier  resolution  of  physiological  states, 
the  organism  or  a  certain  part  thereof  will  have  lost  the  power  of  respond- 
ing to  injury  save  in  one  definite  way.  Under  new  conditions  this  one 
way  may  not  be  regulatory,  yet  it  may  be  the  only  response  possible. 
Thus  may  result  the  formation  under  certain  conditions  of  heteromorphic 
structures,  —  a  tail  in  place  of  a  head,  or  the  like,  from  a  part  of  the 
body  that  (in  normal  development  perhaps)  is  accustomed  to  produce 
such  an  organ.  This  would  again  correspond  to  the  production  of  a 
fixed  reflex  action  in  behavior,  even  under  circumstances  where  this 
action  is  not  regulatory. 

It  appears  to  the  writer  that  the  method  of  form  regulation  recently 
set  forth  in  a  most  suggestive  paper  by  Holmes  (1904)  is  in  agreement 
with  the  general  method  of  regulation  here  set  forth,  and  may  be  consid- 
ered a  working  out  of  the  details  of  the  way  in  which  growth  regulation 
might  take  place  along  these  lines.     Holmes  has  of  course  emphasized 


REGULATION  IN  BEHAVIOR  349 

other  features  of  the  process  in  a  way  that  is  not  called  for  in  the  pres- 
ent work. 

Some  suggestions  as  to  the  possibility  of  regulation  along  the  line  of 
the  selection  of  overproduced  activities  are  found  in  J.  Mark  Baldwin's 
valuable  collection  of  essays  entitled  "Evolution  and  Development." 

It  may  be  noted  that  regulation  in  the  manner  we  have  set  forth  is 
what  in  behavior  is  commonly  called  intelligence.  If  the  same  method 
of  regulation  is  found  in  other  fields,  then  there  is  no  reason  for  refusing 
to  compare  the  action  there  to  intelligence.  Comparison  of  the  regu- 
latory processes  that  are  shown  in  internal  physiological  changes  and  in 
regeneration,  to  intelligence  seems  to  be  looked  upon  sometimes  as  un- 
scientific and  heretical.  Yet  intelligence  is  a  name  applied  to  processes 
that  actually  exist  in  the  regulation  of  movement,  and  there  is  no  a  priori 
reason  why  similar  processes  should  not  occur  in  regulation  in  other 
fields.  Movement  is  after  all  only  the  general  result  of  the  more  recon- 
dite chemical  and  physical  changes  occurring  in  organisms,  and  there- 
fore cannot  follow  laws  differing  in  essential  character  from  the  latter. 
We  are  dealing  in  other  fields  with  the  same  substance  that  is  capable 
of  performing  the  processes  seen  in  intelligent  action,  and  these  could 
not  occur  as  they  do  if  the  underlying  physical  and  chemical  pro- 
cesses did  not  obey  the  same  laws.  In  a  purely  objective  consideration 
there  seems  no  reason  to  suppose  that  regulation  in  behavior  (intelli- 
gence) is  of  a  fundamentally  different  character  from  regulation  else- 
where. 

4.    Summary 

We  may  sum  up  the  fundamental  features  in  the  method  of  individ- 
ual regulation  above  set  forth  as  follows :  — 

The  organism  is  a  complex  of  many  processes,  of  chemical  change,  of 
growth,  and  of  movement ;  these  are  proceeding  with  a  certain  energy. 
These  processes  depend  for  their  unimpeded  course  on  their  relations 
to  each  other  and  on  the  relations  to  the  environment  which  the  pro- 
cesses themselves  bring  about.  When  any  of  these  processes  are  blocked 
or  disturbed,  through  a  change  in  the  relations  to  each  other  or  the 
environment,  the  energy  overflows  in  other  directions,  producing  varied 
changes,  —  in  movement,  and  apparently  also  in  chemical  and  growth 
processes.  These  changes  of  course  vary  the  relations  of  the  processes 
to  each  other  and  to  the  environment;  some  of  the  conditions  thus 
reached  relieve  the  interference  which  was  the  cause  of  the  change. 
Thereupon  the  changes  cease,  since  there  is  no  further  cause  for  them; 
the  relieving  condition  is  therefore  maintained.  After  repetition  of  this 
course  of  events,  the  process  which  leads   to   relief  is  reached  more 


35° 


BEHAVIOR   OF   THE   LOWER   ORGANISMS 


directly,  as  a  result  of  the  law  of  the  readier  resolution  of  physiological 
states  after  repetition.  Thus  are  produced  finally  the  stereotyped 
changes  often  resulting  from  stimulation. 

This  method  of  regulation  is  clearly  seen  in  behavior,  where  its 
operation  is,  in  the  later  stages,  what  is  called  intelligence.  Its  applica- 
tion to  chemical  and  form  regulation  is  at  present  hypothetical,  but 
appears  possible. 


BIBLIOGRAPHY 

The  following  is  a  list  of  the  works  cited  in  the  text.  It  is  not  a  complete 
bibliography  of  behavior  in  lower  animals,  but  will  be  found  to  contain  most  of  the 
more  important  papers  on  the  lowest  groups.  The  authors'  names  are  given  in 
alphabetical  order,  with  their  works  arranged  according  to  the  date  of  their  appear- 
ance. In  the  text  the  works  are  cited  by  the  name  of  the  author  accompanied  by 
the  date;   for  the  complete  title  reference  is  to  be  made  to  the  present  list. 

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worm Allolobophora  fcetida  (Sav.),  as  determined  by  light  of  different  intensities: 
Amer.  Journ.  Physiol.,  IX,  26-34.  —  Allabach,  L.  F.,  1905.  Some  points  regard- 
ing the  behavior  of  Metridium:    Biol.  Bui.,  X,  35-43. 

Bain,  Alexander,  1888.     The  emotions  and  the  will.     604  pp.     London.  — 
Id.,  1894.     The  senses  and  the  intellect.     3d  ed.     New  York.  —  Balbiani,  E.  G., 
1861.     Recherches    sur   les    phenomenes    sexuels    des    infusoires:    Journ.    Physiol. 
(Brown-Sequard),  IV,  102-130;    194-220;   431-448;   465-520  (also  separate,  Paris, 
1862).  —  Id.,  1873.     Observations  sur  le  Didinium  nasutum:    Arch.  d.  Zool.  Exp., 
II,  363-394.  —  Baldwin,  T-  Mark,  1897.     Mental  development  in  the  child  and  in 
the  race.     Methods  and  processes.     2d  ed.     496  pp.     New  York. — Id.,_iqo2.     De- 
velopment and  evolution.     395  pp.     New  York.  —  Bancroft,  F.  W.,   1904.     Note 
on  the  galvanotropic  reactions  of  the  medusa  Polyorchis  penicillata  A.  Agassiz:  Journ. 
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die   Chemotaxis:    Zeitschr.    f.    allg.    Physiol.,   V,    73-94.  —  Beer,    Bethe,    und   v. 
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des  Nervensystems:    Centralb.  f.  Physiol.,  June  10,  5  pp.  —  Bernstein,  J.,  1900. 
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35' 


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INDEX 


Acclimatization  to  stimuli,  in  Amoeba,  24; 
in  Paramecium,  52;  in  sea  anemones, 
207;  general,  294;  to  heat,  101;  to  poisons, 
346. 

Accommodation,  see  adaptiveness  and  regu- 
lation. 

Acids,  collection  in,  by  Paramecium,  65,  67; 
by  other  infusoria,   122. 

Actinia,  taking  of  food  when  cut  in  two, 
227. 

Actinians,   see  sea  anemones. 

Action  system,  Paramecium,  107;  of  infuso- 
ria in  general,  no;  of  Ccelenterata,  189; 
general,   300. 

Activity,  cause  of,  284,  285. 

Adams,  behavior  of  earthworm,  248. 

Adaptiveness  of  behavior,  in  Amoeba,  23;  in 
bacteria,  39;  in  Paramecium,  45,  79. 
109;  of  changes  of  behavior  in  Stentor, 
178;  in  food  reactions  of  Gonionemus, 
221;  in  ccelenterates,  230;  in  reactions 
to  representative  stimuli,  296;  general 
factors,    299,    305,    338-350. 

Adjustment,  342 -(see  adaptiveness  and  regu- 
lation). 

Aiptasia,  reaction  to  local  stimulation,  199; 
setting  of  reaction  by  repetition,  206; 
acclimatization  to  stimuli,  207;  relation 
to  gravity,  211;  food  reactions,  223-226; 
rapid   contraction,    228. 

Allabach,  behavior  of  Metridium,  224. 

Allolobophora,    testing   movements,    247. 

Alternating  electric  currents,  reaction  to, 
in    Paramecium,    83. 

Amoeba  angulata,  5;  proteus,  2,  12,  13; 
velata,   5,   8;    verrucosa,  2,   18. 

Amoeba,  structure,  1 ;  movements,  2 ;  behav- 
ior and  reactions,  6-25;  food  taking,  13- 
19;  relation  of  behavior  to  tropism 
theory,  269;  relation  to  reflexes,  279; 
question   of   consciousness,   336. 

Amylobacter,   30,   32,  38. 

Anaerobic    bacteria,    31,   341. 

Analysis   of   behavior,    283-313. 

Anode,  movement  toward,  in  Paramecium, 
Si,  85,  08;  in  Flagellata,  152;  in  Opa- 
lina,  132,  159;  in  infusoria  in  general, 
163. 

Antholoba,  attachment  to  crabs,  197. 

Antitype,  277. 

Anuraea,  reaction  to  electric  current,  242. 


359 


Association,  in  hermit  crabs,  257,  290;  gen- 
eral,  334. 

Attached  infusoria,  reactions,  116;  complex- 
ity of  behavior,    180. 

Attention,    330. 

Authorities  cited,   351. 

Avoiding  reaction,  in  Paramecium,  47,  53; 
adaptiveness  of,  79 ;  in  Chilomonas,  in; 
in  Euglena,  112;  in  other  flagellates,  113; 
in  other  ciliates,  113;  in  light  reactions, 
149;  relation  to  localization,  117;  relation 
to  reflexes,   279. 

Bacteria,  structure,  26;  movements,  26; 
behavior  and  reactions,  27-40;  relation 
of  behavior  to  tropism  theory,  271;  rela- 
tion to  reflexes,  278;  regulation  in  behav- 
ior,  341. 

Bacterium  chlorinum,  37;  megatherium,  34; 
termo,  30,  32,  ^^,  34. 

Bain,   selection  of  overproduced  movements, 

3°2>    327- 

Balantidium,  reaction  to  chemicals,  122. 

Balbiani,  behavior  of  conjugating  Paramecia, 
104;    use  of  trichocysts,  186. 

Baldwin,  law  of  dynamogenesis,  289;  selec- 
tion of  overproduced  movements,  302, 
327;  organic  selection,  321,  326;  regu- 
lation,   349. 

Bancroft,  reaction  of  infusoria  to  electricity, 
167;    of  medusae  to  electricity,   208,   210. 

Barratt,  reaction  of  Paramecia  to  chemicals, 
64;  theory  of  reaction  to  electricity  (with 
Coehn),   165. 

Bell  of  medusa,  independent  contractility, 
228. 

Beer,  Bethe,  and  v.  Uexkiill,  terminology, 
275;    reflex  and  antitype,  277. 

Bethe,  behavior  of  ants  and  bees,  258. 

Bibliography,   351. 

Bilateral  animals,  relation  of  behavior  to 
tropism  theory,   271,  273. 

Binet,  food  habits  of  infusoria,  186. 

Birukoff,  reaction  of  Paramecium  to  induc- 
tion shocks,   83,  88. 

Blowfly  larva,   behavior,   249. 

Bodo,  reaction  to  chemicals,  124. 

Bohn,  behavior  of  hermit  crabs,  211,  250;  of 
Convoluta,  254;  of  littoral  animals,  255; 
local  action  theory  of  tropisms,  274. 

Botrydium,  reactions  to  light,   143,   144. 


36o 


INDEX 


Bredig,  properties  of  colloids,  317. 

Brittle  star,  behavior  240. 

Bryopsis  swarm  spores,  reactions  to  light,  144. 

Budgett,  theory  of  reaction  to  electric  cur- 
rent  (with   Loeb),    166. 

Bursaria,  avoiding  reaction,  114;  reaction 
to  heat,  126,  305,  318,  322. 

Calvert,  Mrs.  P.  P.,  behavior  of  earthworm, 

247. 

Carbon  dioxide,  reaction  to,  in  Paramecium, 
67,  297;    in  other  infusoria,  122. 

Carchesium,  116;  reaction  to  light,  142;  ces- 
sation of  reaction  to  faint  stimuli,  172. 

Carcinus,  habit  formation,  256. 

Carlgren,  cause  of  reaction  to  electric  cur- 
rent, 165;  ciliary  action  in  sea  anemones, 
222. 

Cataphoric  action,  part  played  in  reaction 
to  electricity,   164. 

Cathode,  movement  toward,  in  Paramecium, 

50,  83;  in  flagellates,  152;  in  ciliates, 
152;  in  Spirostomum,  157;  in  Opalina, 
162;    general,    163. 

"Central   nervous  system"    of  medusas,    189. 
Centrifugal  force,  reaction  to,  in  Paramecium, 

51,  78;    in  other  infusoria,   150. 
Cerianthus,    movement    when    without    food, 

191;  righting  reactions,  195;  reaction  to 
gravity,  195,  210;  reaction  of  hetero- 
morphic  tentacles,   227. 

Chain  reflexes,   251. 

Change  of  conditions  as  cause  of  reactions, 
in  Amceba,  19;  in  bacteria,  29,  37;  in 
Paramecium,  51,  56,  58,  67,  108;  in  other 
infusoria,  123;  in  reactions  to  light,  131, 
i33.  136>  Mi,  145.  2I5I  general,  293, 
333- 

Chemical  processes  in  organisms,  346. 

Chemicals,  reaction  to,  in  Amceba,  9;  in 
bacteria,  28-34;  in  Paramecium,  51,  53, 
54,  62,  120;  in  Hydra,  198,  218;  in  me- 
dusae, 220;  in  sea  anemones,  224;  inter- 
ference with  reaction  to  chemicals,  83, 
96. 

Chilomonas,  structure  and  behavior,  in; 
reaction  to  electric  current,   152. 

Chlamydomonas,  reaction  to  light,  142,  146; 
to  gravity,   149;    to  centrifugal  force,  150. 

Choice,  330,  340;  choice  of  food  in  infuso- 
ria,   183. 

Chromatium,  reactions,  ^^,  35,  36. 

Chromulina,  reactions  to  gravity,  149;  re- 
versal by  heat,    150. 

Chytridium,  reaction  to  light,   142. 

Cilia,  in  infusoria,  41;  observation  of  move- 
ments, 83;  cathodic  reversal  under  electric 
current,  84;  action  in  food  taking  of  sea 
anemones,  222;  reversal  in  sea  anemones, 
223,  224,  227;    cilia  in  sea  urchin,  234. 

Ciliata,  41. 

Cnidaria,  behavior  of,   188-232. 


Cnidocil,  218. 

Coehn  and  Barratt,  theory  of  reaction  to  elec- 
tric  current,    165. 

Ccelenterata,  behavior  of,  18S-232;  reflexes 
in,  133,  279;  relation  to  tropism  theory, 
272. 

Cold,  reaction  to,  in  bacteria,  37;  in  Para- 
mecium, 51,  53,  70;  in  other  infusoria, 
124;    effect  on  Hydra,  205. 

Coleps,  lack  of  reaction  to  gravity,  150. 

Colloids,  dependence  of  properties  on  his- 
tory,   317,    334. 

Color,  reaction  to,  in  Amceba,  n;  in  bac- 
teria, 36,  341;  in  Euglena,  140;  in  Hydra, 
212. 

Colorless  infusoria,  usual  lack  of  reaction  to 
light,  12S;    cases  of  reaction  to  light,  142, 

333- 

Colpidium,  avoiding  reaction,  115;  collec- 
tion in  acids,  122  ;  lack  of  reaction  to  grav- 
ity, 150;    reaction  to  electric  current,  155. 

Colpoda,  lack  of  reaction  to  gravity,  150. 

Combinations  of  stimuli,  in  infusoria,  92. 

Compensatory  movements,   75. 

Conduction  of  stimulation,  in  ccelenterates, 
228;    in   Protozoa,    262. 

Condylactis,  relation  to  gravity,  211. 

Congenital   variations,    319,   320. 

Conjugation,  behavior  during,  102,  182. 

Consciousness,   328,   334,  335,   340. 

Contact  reactions,  in  Amceba,  6;  in  bacteria, 
27,  37;  in  Paramecium,  51,  54,  59,  60; 
in  other  infusoria,  117;  interference 
with  other  reactions,  92-96,  119,  133; 
cause  of   interference,    120. 

Contraction,  in  response  to  stimuli,  in  Para- 
mecium, 89;  in  other  infusoria,  114;  in 
Ccelenterata,  197;  spontaneous  contrac- 
tions in  infusoria,  181;  in  Hydra,  189; 
in  medusas,  191;  rapid  contraction  in 
Aiptasia,  228;  local  contractions  in  ccelen- 
terates,  231;  relation  to  tropism  theory, 
272;  setting  of  contractions  through  repe- 
tition in  sea  anemones,  206. 

Convoluta,  habit  formation,  255,  333;  depen- 
dence of  reaction  to  gravity  on  past  his- 
tory,   258. 

Correlation  of  behavior  in  different  parts  of 
ccelenterate  body,  227,  229;  in  sea  urchin, 
252;    in  starfish,  239. 

Corymorpha,  reaction  to  gravity,  210;  reac- 
tion  of   tentacles,    222. 

Crab,  habit   formation,  256,  290. 

Crayfish,  habit  formation,  255,  290. 

Creeping  infusoria,  reactions,  114;  complex- 
ity of  behavior,   180. 

Crustacea,    habit    formation,    255,    290,    333. 

Cryptomonas,  reaction  to  light,  142,  143,  146; 
to  electric  current,   152. 

Currents,  protoplasmic,  in  Amceba,  4;  cur- 
rents due  to  cilia  in  infusoria,  46,  60,  131; 
observation    of    these    currents,    83;     cur- 


INDEX 


361 


rents  in  reaction  to  electricity,  85;  reac- 
tion to  water  currents  in  Paramecium,  73. 

Cutleria  swarm  spores,  reaction  to  light,  142, 
146. 

Cyclidium,  collection  in  acids,   122. 

Cysts  of  Euglena,  as  food  for  Amoeba,  12. 

Daily  life  of  Paramecium,  104. 

Dale,  reaction  of  infusoria  to  water  currents, 
75 ;    to  chemicals,   122. 

Davenport,  reaction  of  Amoeba  to  light,  n, 
21;  of  Paramecium  to  gravity,  76;  of  in- 
fusoria to  chemicals,  122;  diagram  of 
tropism  theory,  268;   terminology,  275. 

Desire,  331. 

Development  of  behavior,  314-327. 

Didinium,  food  habits,  91,  185;  discharge  of 
trichocysts,    186. 

Discrimination,    304,    315,    329. 

Driesch,  chain  reflexes,  251;  tropism  theory, 
266;    reflex,   278;    vitalism,   338. 

Driving  Amoeba,   6. 

Drying,  reaction  to,  in  flatworm,  243. 

Earthworm,  testing  movements,  247;  reac- 
tion to  light,  248. 

Echinoderms,  behavior,  234,  238;  relation 
to  tropism  theory,  272. 

Ectosarc,  2,  43;  contraction  in  Paramecium,  89. 

Electricity,  reaction  to,  in  Amceba,  12,  23,  24; 
in  bacteria,  37;  in  Paramecium,  51,  So 
(induction  shocks,  81;  alternating  cur- 
rents, 83,  87  ;  constant  current,  83 ;  inter- 
ference with  reaction  to  electricity,  94,  96, 
119);  in  other  infusoria,  151  (induction 
shocks,  151;-  constant  current,  152); 
lack  of  reaction  in  Euglena,  152;  reaction 
in  Colpidium,  155;  in  Spirostomum,  157; 
in  Opalina,  159;  summary  on  infusoria, 
163;  theories,  164;  reaction  in  ccelen- 
terates,  208;  in  rotifers,  242;  agreement 
with  tropism  theory  in  infusoria,  271. 

Elemental  life,   260. 

Endosarc,   2,  43. 

Engelmann,  reaction  of  Pelomyxa  to  light, 
11;  behavior  of  bacteria,  30,  35,  36,  39; 
reaction  of  Euglena  to  shading  parts  of 
body,  136;  reaction  to  light  in  Parame- 
cium bursaria,    142;     terminology,   275. 

Epistylis,  reaction  to  ultra-violet  light,  142; 
cessation  of  reaction  to  weak  stimuli,  172. 

Ether,  collection  of  bacteria  in,  ^3- 

Euglena,  structure  and  reactions,  102,  134; 
reactions  to  light,  134,  294;  spiral  path, 
138;  reaction  to  gravity,  149;  to  centrifu- 
gal force,  150;  no  reaction  to  electric 
current,   152. 

Exploratory  movements,  in  Lacrymaria,  181; 
in  Hydra,  189,  204;  in  medusae,  220;  in 
sea  anemones,  222;  in  Planaria,  243- 
245;  in  other  invertebrates,  246-250 
(see  trial  movements). 


Famintzin,  reaction  of  flagellates  to  light, 
140. 

Fatigue,  in  infusoria,  100,  172;    general,  331. 

Fear,   332. 

Fern  spermatozoids,  reaction  method,  121; 
Weber's  law,   123. 

Final   causes,   344. 

"Fishing"  in  Gonionemus,  192,  211,  214. 

Fission,  behavior  during,   102. 

Flagella,  in  bacteria,  26;  in  infusoria,  41,  60, 
in. 

Flagellata,  41;  movements  and  reactions, 
in;    reactions  to  electricity,   119,   152. 

Flatworm,  localization  of  reactions,  236; 
testing  movements,  243 ;  righting  reac- 
tion, 245;  physiological  states,  253; 
habit  formation,  254. 

Food,  behavior  in  obtaining,  Amoeba,  12- 
19,  24,  25;  Paramecium,  46,  183;  Sten- 
tor,  171;  in  other  infusoria,  118,  182; 
Gonionemus,  192,  219;  in  ccelenterates 
in  general,  216;  Hydra,  216;  medusae, 
219;  sea  anemones,  221;  sea  urchin, 
235;  flatworm,  246;  mollusk  (Nassa), 
247;  food  habits  in  general,  331;  lack  of 
food,  in  infusoria,  101;  in  Hydra,  189; 
in  Cerianthus,  196;  rejection  of  food  in 
sea  anemones,  202 ;  relation  of  food 
reactions  to  reaction  to  light,  in  parasitic 
infusoria,   142;    in  Hydra,  213. 

Form  regulation,   348. 

Free  infusoria,   simplicity  of  behavior,   180. 

Gamble  and  Keeble,  behavior  of  Convoluta, 

255- 

Garrey,  kinesis,  275. 

Gonionemus,  "fishing,"  192;  relation  to 
gravity,  211,  reaction  to  light,  214; 
food  reactions,  219;  chemical  stimuli, 
220;  mechanical  stimuli,  220;  reactions 
of  separated  parts,  227;  adaptiveness  of 
reactions,    221,    230. 

Gravity,  reaction  to,  in  bacteria,  37;  in  Para- 
mecium, 51,  75;  in  other  infusoria,  150; 
interference  with,  in  infusoria,  96,  150; 
reaction  in  ccelenterates,  195,  210;  in 
hermit  crabs,  211;  in  Convoluta,  255;  de- 
pendence on  experience  in  Convoluta, 
258;  general  effects  of  gravity  on  organ- 
isms,   211. 

Growth,  regulation  of,  348. 

Habit,  2,22,. 

Habit    formation,    sea     anemone    (?),    207; 

starfish,  241;    Convoluta  (flatworm),  254; 

Crustacea,   255;    retention  of  habit,    256. 
Haematococcus,    reaction   to   light,    142,    146; 

to   gravity,    149. 
Halteria,    reaction,    115. 
Harper,  behavior  of  earthworm,  247,  24S. 
Harrington  and  Learning,  reaction  of  Amoeba 

to  light,   1 1,  20,  24. 


36: 


INDEX 


Heat,  reaction  to,  in  Amceba,  10;  in  bac- 
teria, 37;  in  Paramecium,  51-53,  70,  305; 
in  other  infusoria,  124,  305;  in  Hydra, 
204;  in  rotifers,  242;  in  flatworms,  244; 
interference  with  other  reactions,  150; 
interference  of  other  reactions  with  reac- 
tion to  heat,  93. 

Hermit  crabs,  temporary  reaction  to  gravity, 
211;  seeking  shells,  250;  formation  of 
association  and  habit,   257,   290. 

Hertel,  reactions  to  ultra-violet  light,  in 
Paramecium,  72;  in  other  infusoria,  142; 
in   Hydra,    213. 

Heteromorphic  tentacles,  behavior,  227. 

Hobhouse,  reflex,  278;  selection  from  varied 
movements,    327. 

Hodge  and  Aikins,  changes  in  behavior  in 
Vorticella,  179;  duration  of  modifica- 
tion, 254;  continuous  activity  of  Vorti- 
cella,    181. 

Holmes,  trial  movements  in  lower  animals, 
247-250;  random  movements,  251,  254; 
form    regulation,    348. 

Holt  and  Lee,  tropism  theory  in  reactions  to 
light,   266,   269. 

Hunger,  infusoria,  101;  Hydra,  189,  205,  219; 
sea  anemones,  191,  224;  Planaria,  253;  in- 
vertebrates in  general,   252;   general,  295, 

33*- 

Hunter  ciliates,    184. 

Hydra,  nervous  system,  189;  rhythmic  ac- 
tivity, 189,  285;  locomotion,  iqo;  posi- 
tion, 193;  righting  reaction,  193;  local 
contractions,  198,  272;  locomotor  reac- 
tions, 203;  reactions  to  electric  current, 
208;  to  light,  212;  to  chemicals,  198, 
218;  food  reactions,  217;  nematocyst 
discharge,    218;     hunger,    219. 

Hydroid,  reaction  to  gravity,  210;  reaction 
of  tentacles,    222. 

Hydromedusse,  reactions  of  separated  mar- 
gin and  bell,  227   (see  medusa). 

Hypotricha,  reaction  method,  53,  114;  creep- 
ing, 118;  reaction  to  heat  and  cold,  124; 
to  electricity,    154. 

Independence  of  parts  of  body,  in  ccelen- 
terates,  227;    in  sea  urchin,  235. 

Individual  selection,  relation  to  natural  selec- 
tion, 324. 

Induction  shocks,  reaction  to,  infusoria,  81, 
102,   104,   151;    ccelenterates,  208. 

Infusoria,  41;  behavior,  41-187;  behavior 
under  natural  conditions,  179;  food 
habits,    183;     relation    to    tropism,    270. 

Inhibition,  release  of,  as  determining  move- 
ment,  284. 

Injury,  relation  of  reactions  to,  in  Amceba, 
23;  in  bacteria,  33;  in  Paramecium,  52, 
63,  109  (see  regulation,  and  interference 
with  processes). 

Instincts,   237. 


Intelligence,  334,  343;  relation  to  natural 
selection,    324,    345;     to    regulation,    349, 

35°- 

Interference  with  internal  processes  as  cause 
of  reaction,  in  Amceba,  n,  20;  in  bac- 
teria, 39,  341;  general,  295,  342,  346; 
interference  of  stimuli,  92,  119,  150. 

Internal  factors  in  behavior,  283. 

Invertebrates,  lower,  general  features  of  be- 
havior,   233-259. 

James,  reflex,   278,   280,  281. 
Jellyfish,  see  medusa. 

Jensen,  reactions  to  gravity  in  infusoria,  76, 
149. 

Kinesis,   275. 

Kiihne,  polarizing  effects  of  electric  current, 
167. 

Lacrymaria,  reaction  to  induction  shock, 
151;    trial  movements,   181. 

Lagynus,  food  habits,   187. 

Le  Dantec,  life  processes  of  Protozoa  and 
Metazoa,    260. 

Learning,  relation  of  change  of  behavior  in 
infusoria    to,    178;     in    crustaceans,    255. 

Leech,  trial  movements,  247 ;  reaction  to 
light,     248. 

Leidy,  taking  food  in  Amceba,  15,  19. 

Light,  reaction  to,  Amceba,  1 1 ;  bacteria, 
35-37,  341;  Paramecium,  72;  Stentor,  128; 
Euglena,  134;  other  infusoria,  141; 
swarm  spores,  143;  Ccelenterata,  212; 
Hydra,  212;  Gonionemus,  214;  Roti- 
fera,  242;  earthworm,  247;  leech,  248; 
blowfly  larva,  249;  in  colorless  organ- 
isms, 142,  213,  333;  tropism  theory  for 
light  reactions,   266,   268,   269. 

Literature   list,   351. 

Localization  of  reactions,  in  Amceba,  20; 
Paramecium,  51,  52;  in  other  infusoria, 
117;  different  methods,  307;  relation  to 
tropism  theory,  266,  274. 

Localized  reactions  in  ccelenterates,  198,  231; 
in  theory  of  tropisms,  266,  274. 

Locomotion,  in  Hydra,  191;  in  sea  anemones, 
191. 

Locomotor    reactions    in    Ccelenterata,    203. 

Loeb,  behavior  of  Cerianthus,  191,  195; 
localization  in  medusre,  200;  indepen- 
dent activity  of  parts  of  body  in  Ccelen- 
terata, 227,  228;  function  of  nervous 
system  in  medusa?,  229;  chain  reflexes, 
251;  function  of  nervous  system,  263; 
tropism  theory,   266,  269. 

Loeb  and  Budgett,  theory  of  reaction  to  elec- 
tricity,   166. 

Loxocephalus,    spontaneous    collections,    122. 

Loxodes,  avoiding  reaction,    113. 

Loxophyllum,   avoiding   reaction,    113. 

Ludloff,  reactions  to  electricity,  84,   167. 


INDEX 


3*3 


Lyon,  reaction  to  currents,  74;  to  gravity, 
77;    to  centrifugal  force,  78. 

Manubrium,  localizing  reactions,  200;  food 
reactions,  220;  independent  reactions, 
227. 

Massart,  reactions  of  bacteria,  34,  37;  dis- 
charge of  trichocysts,  90;  interference  of 
heat  and  contact  reactions,  93;  reaction 
of  Polytoma,  123;  reversal  of  reaction  to 
gravity  by  heat,  150;    nomenclature,  275. 

Mast,  reactions  of  bacteria,  37;  local  stimu- 
lation with  heat,  198;  behavior  of  Hydra, 
203,  205  ;   reaction  of  flatworm  to  heat,  245. 

Maupas,   food  habits  of  infusoria,    182,    186. 

Mechanical  stimulation,  in  Amoeba,  6;  in 
bacteria,  27,  37;  in  Paramecium,  51,  54, 
59;  in  other  infusoria,  117;  in  Hydra, 
204;  in  medusae,  220;  interference  with 
other  stimuli  in  infusoria,  92-96. 

Medusae,  nervous  system,  189;  rhythmical 
contractions,  191,  227;  food  habits,  192, 
219;  reaction  to  local  stimulation,  199, 
200;  reaction  to  electric  current,  210; 
to  gravity,  211;  to  light,  214;  to  chemi- 
cals, 220;  behavior  of  separated  pieces, 
227;  relation  of  behavior  to  tropism  the- 
ory,   272. 

Memory.   333. 

Mendelssohn,  temperature  reactions,  70; 
optimum  for  infusoria,  127;  change  of 
optimum,    101. 

Metabolism,  relation  of  behavior  to,  in  bac- 
teria, 36,  39;  in  Coelenterata,  231;  in 
invertebrates  in  general,  251;  relation  to 
movement,  284';  relation  to  changes  in 
physiological  state,  286,  287;  relation  to 
positive  reactions,  295;  general,  299, 
34o,   341- 

Metazoa  and  Protozoa,  188;  comparison  of 
behavior,    260-264. 

Metridium,  movement  from  internal  causes, 
191;  relation  to  gravity,  211;  food  reac- 
tions, 222,  224,  225;  fatigue,  226;  reac- 
tions of  separated  tentacles,  227. 

Microthorax,   avoiding  reaction,    115. 

Miyoshi,  reactions  of  bacteria,  32. 

Modifiability  of  behavior,  Amoeba,  24;  bac- 
teria, 39;  Paramecium,  100;  Stentor, 
170;  sea  anemones,  206,  207,  226;  Coe- 
lenterata, 231,  232;  invertebrates,  237, 
250;  Convoluta  (flatworm),  255;  Crus- 
tacea, 255-257;  higher  invertebrates, 
258;  general,  258,  317;  laws  of,  286-291; 
modifiability   in    colloids,    317. 

Moebius,  behavior  of  Nassa,  247. 

Mollusks,  trial  movements,   247. 

Monas,  reaction  to  light,  36. 

Moore,  reactions  of  infusoria  to  gravity,  77, 
96;    lack  of  food,  101. 

Morgan,  C.  L.,  trial  and  error  in  higher  ani- 
mals, 250. 


Morgan,   T.   H.,   variability   in  regeneration, 

348. 
Motile    touch,    reaction    of    Gonionemus    to, 

221,    230. 
Movement     spontaneous,     283 ;      cause     of, 

284,    2S5. 
Myxomycetes,  reaction  to  light,   12. 

Naegeli,  movement  and  reactions  of  flagel- 
lates, in,  113;  spiral  movement  in  swarm 
spores,    143. 

Nagel,  food  reactions  in  sea  anemones,  224. 

Nassa,  behavior  in  finding  food,  247. 

Natural  selection,  320;  relation  to  individ- 
ual selection  or  intelligence,  324,  325,  345; 
part  played  in  behavior,  327. 

Negative  reaction,  in  Amoeba,  6,  23;  in 
bacteria,  27,  28;  in  infusoria,  53,  117; 
general,   301. 

Nematocysts,  action  in  food  taking,  218. 

Nervous  system,  of  Coelenterata,  189;  con- 
duction by,  in  ccelenterates,  228;  func- 
tion in  ccelenterates,  230;  specific  prop- 
erties and  general  functions,  260-264; 
behavior  without  a  nervous  system,   261. 

Nomenclature,    274-276. 

Nucleus,  in  Amoeba,  2;    in   Paramecium,  43. 

Nutritive  processes,  relation  of  behavior  to, 
see  metabolism. 

Nyctotherus,  avoiding  reaction,  114;  reac- 
tion to  chemicals,   122. 

Oltmanns,   terminology,   275. 
Opalina,  avoiding  reaction,   114;    reaction  to 
chemicals,    122;    to  electric  current,    156, 

i59- 

Ophidomonas,  reaction  to  light,  36. 

Ophryoglena,  lack  of  reaction  to  gravity,  150. 

Optimum,     in     bacteria,     31;      Paramecium, 
56,  66;    for  temperature,  71,  127;    change 
of  optimum,    101;  optimum  in  other  in- 
fusoria, 123,  127;    optimum  in  light  reac- 
tions,  141,   148;    general,   295. 

Organic  selection,   321. 

Orientation,  Amoeba,  22,  269;  Paramecium, 
73  (by  exclusion,  72);  relation  between 
orientation  reactions  and  others  in  infuso- 
ria, 78;  no  position  of  symmetry  in  infu- 
soria, 79;  orientation  by  exclusion  in 
Oxytricha,  126;  orientation  to  light,  134, 
138-140;  to  electric  current,  153,  163; 
in  rotifera,  242;  orientation  to  light  in 
earthworm,  247,  24S;  in  blowfly  larva, 
249;  fundamental  feature  in  tropism, 
264;    how  brought  about,  267. 

Oscillaria,  as  food  for  Amoeba,  19. 

Osmotic  pressure,  reaction  to,  in  bacteria, 
34;  in  Paramecium,  63;  in  other  infuso- 
ria,   124. 

Ostwald,  chemical  processes  in  organisms, 
340. 

Oxygen,  reaction  to,  bacteria,  28-31,  39,  341; 


364 


INDEX 


Paramecium,  66,  340;  infusoria  in  gen- 
eral, 124;  Hydra,  216;  relation  to  reac- 
tion to  light  in  Paramecium  bursaria,  142; 
general,  340. 
Oxytricha,  avoiding  reaction,  114;  sponta- 
neous collections,  122;  reaction  to  heat 
and  cold,  125;  transverse  position  in 
electric  current,   154. 

Pain,   332,   340. 

Paramecium,  structure,  41;    movements,  44; 

behavior  and  reactions,   44-109;    relation 

of  behavior  to   reflexes,   279;    relation  to 

consciousness,  336. 
Paramecium  bursaria,  reaction  to  light,   142, 

340;    to  gravity,    149- 
Parasitic  infusoria,  reaction  to  light,  142,  333. 
Parker,    reversal    of   cilia   in   sea    anemones, 

224;      reaction    of    separate    parts,    227; 

conduction  of  stimulation,   229. 
Parker  and  Arkin,  behavior  of  earthworm,  248. 
Pawlow,   modifiability  of  action  in  digestive 

glands,    347. 
Pearl,  reaction  to  electric  current,   Chilomo- 

nas,    152;    Colpidium,   155;    Hydra,   208; 

cause  of  reaction  to  electric  current,  165; 

behavior  of   Planaria,  236,  243,   245,  253, 

273- 

Pedicellariae,  234;    behavior,  235,  238. 

Pelomyxa,  reaction  to  light,   n. 

Penard,  movements  of  Amoeba,  6,  8. 

Perception,   329. 

Perichoeta,   reaction  to  light,   248. 

Peridinium,  reaction  to  electric  current,   152. 

Perkins,  behavior  of  Gonionemus,   192. 

Pfeffer,  behavior  of  bacteria,  32,  33,  34,  38; 
of  fern  spermatozoids  and  flagellates, 
123,    124;    tropisms,    275;     nomenclature, 

275- 

Physiological  states,  dependence  of  behav- 
ior on,  Stentor,  178;  ccelenterates,  229, 
231;  invertebrates  in  general,  251;  flat- 
worm,  253;  Protozoa  and  Metazoa,  263; 
higher  animals  and  man,  331;  relation  to 
reflexes,  282 ;  changes  of  physiological 
state,  287;  law  of  change,  291;  develop- 
ment in  physiological  states,  316;  gen- 
eral,   286-291. 

Planaria,  localization  of  reaction,  236;  test- 
ing movements,  243;  righting  reaction, 
245;  physiological  states,  233;  relation 
to  tropism  theory,  273. 

Plasmolysis,   34. 

Pleasure,  332,  340. 

Pleuronema,  reaction  method,  115;  reaction 
to  light,  142. 

Poisons,  collection  of  bacteria  in,  ^^. 

Polarizing  effect  of  electric  current,  167. 

Polyorchis,   reaction  to  electric  current,   210. 

Polytoma,  reaction  to  chemicals,  123;  to 
gravity,  149. 

Polytomella,  reaction  to  electric  current,  152. 


Positive  reaction,  in  Amoeba,  8,  23;  bacteria, 
28;  Paramecium,  54,  60,  65;  in  other 
infusoria,  121;    general,  295,  309. 

Preyer,  behavior  of  starfish,  239;  habit  for- 
mation in  starfish,  241 ;  varied  physio- 
logical states,   253. 

Prism,    Strasburger's   experiments   with,    145. 

Protozoa,  behavior,  1-187;  reflexes  in,  233; 
relation  to  tropism  theory,  269-271; 
comparison  with  behavior  of  Metazoa, 
260-264. 

Pseudopodia,  1,  4;    reaction  of  single  one,  15. 

Psychic  behavior,  relation  to  behavior  of 
lower  organisms,   329. 

Purpose,  343. 

Putter,  interference  of  heat  and  contact  reac- 
tions, 93;  of  contact  and  reaction  to  elec- 
tricity, 119;  variability  of  contact  reac- 
tion,   100;    symptomatology,   300. 

Quieting  infusoria,  81,  83. 

Radl,  reaction  to  gravity,  77;  theory  of 
tropisms  in  reaction  to  light,  274. 

Random  movements,  251,  254  (see  trial  move- 
ments). 

Reaction,   6,   283. 

Reflexes,  232;  in  Protozoa  and  Ccelente- 
rata,  233;  in  sea  urchin,  234,  235;  in  star- 
fish, 236;  in  flatworm,  236,  254;  in  higher 
animals,  237;  relation  to  modifiability, 
258;  definition,  277;  part  played  in  be- 
havior of  lower  animals,   277-282. 

Regeneration,    variation    in    processes,     348. 

Regulation,  299,  301 ;  how  brought  about  in  be- 
havior, 338-350;  in  other  fields,  345;  in 
chemical  processes,  346;  in  growth,  348; 
non-regulatory  behavior,  345  (see  adap- 
th'cness). 

Rejecting  reaction  of  sea  anemones,  202. 

Rejection  of  unsuitable  food,  in  infusoria, 
183;    in  sea  anemones,  202. 

Representative  stimuli,   296,  316,  333. 

"Republic  of  reflexes,"    235. 

Resolution  of  physiological  states,  law  of, 
291,  314,  334;    part  played  in  regulation, 

343- 

Respiration,  relation  of  habits  to,  in  Parame- 
cium bursaria,   142,  340;    in  Hydra,   216. 

Reversal  of  reactions,  as  stimulus  becomes 
stronger,  262  (see  optimum);  reversal  of 
cilia  in  sea  anemones,  224. 

Rhumbler,  currents  in  Amceba,  4,  5 ;  reac- 
tions of  Amoeba  to  food,   n,   19,   20,   25. 

Rhythmical  contractions,  in  Yorticella,  1S1 ;  in 
Hydra,  189;  in  medusa,  191;  in  margins 
and  bell  of  medusae  when  separated,  227; 
rhythmical  activity  of  Convoluta  as  habit, 

255- 
Righting    reaction,    in    Hydra,    193;     in    sea 
anemones,  195;    in  starfish,  239;    in  flat- 
worm,    245. 


INDEX 


36: 


Roesle,  reaction  to  induction  shocks  in  infu- 
soria,   82,    151. 

Rolling  movement  in  Amoeba,  2. 

Romanes,  localization  in  medusa,  200;  reac- 
tion of  parts  of  medusa;,  227;  nervous 
conduction  in  medusae,  228,  229;  behav- 
ior of  starfish,   241. 

Rothert,  reactions  of  bacteria,  31,  32,  37; 
reaction  method  in  flagellates,  121;  kine- 
sis,   275. 

Rotifera,  avoiding  reaction,  236;  reactions 
to  stimuli,  242. 

Roux,  polarizing  effect  of  electric  current, 
167. 

Sagartia,  reaction  to  gravity,  196,  210;  to 
local  stimulation,  199;  finding  food,  222; 
taking  indifferent  bodies,  224;  reactions 
of  separate  tentacles,    227. 

Saprolegnia,  swarm  spores,  reaction  method, 
121. 

Schwarz,    reaction   to   centrifugal   force,    150. 

Sea  anemones,  nervous  system,  189;  loco- 
motion, 191;  effects  of  hunger,  191; 
righting  reaction,  195;  reaction  to  grav- 
ity, 195,  210;  attachment  to  crab,  197; 
localized  reactions,  199;  rejecting  reac- 
tion, 202;  direction  of  movement,  206; 
setting  of  reaction  by  repetition,  206; 
acclimatization  to  stimuli,  207;  food 
habits,  221;    part  played  by  cilia,  222. 

Sea  urchin,  reflexes,  234;  reaction  by  varied 
movement,  238;  dependence  of  behavior 
on  physiological  states,  252;  modifiability 
of   behavior,    252. 

Selection  of  conditions  resulting  from  varied 
movements,  Amceba,  22;  bacteria,  40; 
Paramecium,  79,  108;  flagellates,  112; 
ciliates,  115;  ccelenterates,  230;  in  in- 
vertebrata  in  general,  238;  rotifers,  242; 
flatworms,  246;  in  Protozoa  and  Metazoa, 
263;  production  of  regulation,  339,  342; 
general,  302. 

Sensitiveness  of  different  parts  of  body,  in 
infusoria,  59,  82,  117,  133,  136;  compari- 
son with  sense  organ,  262. 

Simultaneous  stimuli,  effect  on  infusoria,  92, 
180. 

Sleep,    331. 

Smith,  behavior  of  earthworm,  247,  254. 

Solids,  reaction  to,  Amceba,  6;  bacteria,  27, 
37;  Paramecium,  51.  54,  59-62".  other 
infusoria,  117;  interference  with  other 
reactions,    92-96,    119. 

Sosnowski,   reactions  of  infusoria  to  gravity, 

77,   oo- 

Spaulding,  association  and  habit  formation 
in  hermit  crabs,  257;    reflex,  282. 

Spectrum,  behavior  of  bacteria  in,  36;  of  Eu- 
glena,  140. 

Spencer,  selection  of  overproduced  move- 
ments,   302,    327. 


Spermatozoids  of  fern,  reaction  method,  121; 
Weber's  law,   123. 

Spiral  movement,  bacteria,  27;  Paramecium, 
44,  46,  58;  other  infusoria,  no;  flagel- 
lates, in;  swarm  spores,  143;  effect  on 
relation  to  light,   133,   13S. 

Spirillum,   behavior,   27-29,  ^^<  34- 

Spirostomum,  avoiding  reaction,  114;  at- 
tachment by  mucus,  116,  11S;  relation 
to  gravity,  149;  reaction  to  induction 
shocks,    151;     to    constant    current,    157. 

Spontaneous  activity,  in  Protozoa  and  Meta- 
zoa, 261;  in  ccelenterates,  189;  general, 
283;  spontaneous  collections  of  infusoria, 
68,     122. 

Starfish,  reflexes,  236;  variable  reactions, 
239;  righting  reaction,  238;  setting  of 
reaction   by   repetition,   241. 

Statkewitsch,  reaction  of  Paramecium  to 
water  current,  75;  reaction  to  induction 
shocks,  81,  83,  88,  151;  to  constant  cur- 
rent, 84;  to  alternating  currents,  87; 
quieting  infusoria,  Si,  83;  discharge  of 
trichocysts,  90,  104;  cataphoric  action, 
165;  cause  of  reaction  to  electric  current, 
167. 

Stentor,  avoiding  reaction,  113;  attached 
Stentors,  116;  reaction  to  light,  128,  142; 
behavior  when  attached,  171;  modifica- 
tion of  reactions,  1 71-179,  233'y  tube 
formation,  176;  choice  of  food,  183; 
relation  of  behavior  to  reflexes,  279; 
changes  in  physiological  state,  2S7;  laws 
of  change,  290. 

Stimuli,    6,    293. 

Stoichactis,  rejecting  reaction,  201;  reaction 
to  gravity,   211;    food  reactions,   223-226. 

Strasburger,  reaction  method  in  swarm  spores, 
113;  reaction  of  swarm  spores  to  light, 
143;  experiments  with  prism,  145;  ter- 
minology,  275. 

Stylonychia,  avoiding  reaction,  114;  creep- 
ing on  surface,  118;  reaction  to  electric 
current,    154;    food  habits,   184. 

Subjective  states,  328,  331. 

Summation  of  stimuli  in  Protozoa,   83,   262. 

Surface  tension,  currents  due  to,  4. 

Swarm  spores,  reaction  method,  113;  reac- 
tion to  light,    142,    143. 

Temperature  reactions,  Amceba,  10;  bacteria, 
37,  Paramecium,  51,  54,  55,  70;  other  infu- 
soria, 124;  interference  with  temperature 
reactions,  93;  optimum  in  infusoria,  127; 
reaction  in  Hydra,  204;    in  flatworm,  243. 

Tentacles,  stimulation  of,  Hydra,  198;  sea 
anemones,  199;  medusa?,  200;  methods 
of  contraction  and  bending,  198,  199; 
movements  in  medusae,  220;  in  sea  anem- 
ones, 222;  behavior  of  separated  tenta- 
cles,   227. 

Terms    employed    in    animal    behavior,    274. 


366 


INDEX 


Thorndike,  trial  and  error  in  higher  animals, 
250. 

Tiaropsis,  localizing  reaction,  200. 

Titchener,  objective  criteria  of  conscious- 
ness,   278. 

Tonus,  252,  263. 

Torre}-,  behavior  of  Sagartia,  196,  199,  210, 
222,  224,  227;    of  Corymorpha,  210,  222. 

Trachelomonas,   reaction  to  electric   current, 

152. 

Tradescantia  cells,  effect  of  electric  current, 
167. 

Transverse  position,  of  Paramecia  in  alter- 
nating electric  currents,  87;  in  constant 
current,  95;  of  Hypotricha  in  constant 
current,  154;  of  Spirostomum,  158;  in- 
fusoria in  general,  163. 

Trepomonas,  reaction  method,  121. 

Trial  movements,  Amceba,  22;  Paramecium, 
48,  106,  108;  Stentor,  177;  Lacrymaria, 
181;  in  hunter  ciliates,  186;  Hydra,  204; 
medusa?,  220;  sea  anemones,  222;  Cce- 
lenterata  in  general,  230;  in  inverte- 
brates in  general,  238,  240,  251;  flatworms, 
243,  245,  246;  earthworm,  247;  leech,  248; 
blowfly  larva?,  249;  hermit  crabs,  250; 
higher  animals,  250,  272;  general,  305; 
339-   342. 

Trichocysts,  43;  discharge,  90,  82,  186;  func- 
tion,  90. 

Tropisms,  237;  local  action  theory  of,  265- 
274;    various  definitions,   274,   275. 

Tube,  of  Stentor,  170;  formation  of,  176; 
in  other  infusoria,  181. 

Uexkiill,  v.,  behavior  of  sea  urchin,  234,  238, 

252;    reflex,    281. 
Ultra- red  light,  reaction  of    bacteria    to,  36; 

ultra-violet  light,  reaction  to,   72,  142. 
Ulva,  swarm  spores,  reaction  to  light,  143,  144. 


Urocentrum,     attachment     by     mucus,     116, 

118. 
Urostyla,  reaction  to  gravity,  149. 

Variability  in  reactions,  bacteria,  38;  Para- 
mecium, 49,  98,  279;  other  infusoria,  123; 
Stentor,  176;  coelenterates,  231;  echino- 
derms,    238,    239. 

Variations,  individual,  in  behavior,  319,  321. 

Verworn,  reaction  of  Amceba  to  electricity, 
24;  reaction  of  Pleuronema  to  light,  142; 
of  flagellates  to  electricity,  152;  theory 
of  reaction  to  electricity,  167;  tropism  the- 
ory, 266,  267,  269. 

Vitalism,  338,  344. 

Vorticella,  116;  changes  in  reactions,  179; 
duration  of  modifications,  179,  254; 
spontaneous  contractions,  181,  285,  286; 
no  periods  of  rest,  181,  284;  rejection  of 
unsuitable  food,   184. 

Wagner,   behavior  of  Hydra,    191,    203,   217. 

Wallengren,  lack  of  food  in  infusoria,  101; 
lack  of  salts,  101;  reaction  to  electric 
current  in  Spirostomum,  157;  in  Opa- 
lina,    159. 

Water  currents,  reaction  to,  in  Paramecium, 

73- 
Weber's  law,  in  bacteria,  38;   in  fern  sperma- 

tozoids,    123;    general,   294. 
Wilson,   reaction  of  Hydra  to  light,   212;    to 

oxygen,    216;    food  reactions,   219. 
Wundt,  reflex,  278. 

Yerkes,  behavior  of  Gonionemus,  192,  21  r, 
214,  219,  227;  habit  formation  in  Crus- 
tacea, 255;  nomenclature,  275;  modi- 
fiability  of  behavior,  290,  291. 

Yerkes  and  Huggins,  habit  formation  in 
Crustacea,  255.